What does it actually mean?

What is that "YKK" that you see on your zippers? 10 codes explained

Have you noticed "YKK" stamped on your zippers or that "RSVP" on an invitation? What does the mysterious "SSSS" on your boarding pass mean? These little letters and codes are everywhere, but if you stop and think about it, there are plenty whose meaning we don’t really know. Behind many of them are surprising stories, foreign languages, old technologies, and even a few myths. Here are 10 everyday codes and abbreviations you’ve probably seen countless times without knowing what they actually mean.

You’ve probably noticed that almost every zipper on your clothes has the letters "YKK" stamped on it. But have you ever wondered what those three letters actually mean?

They stand for Yoshida Kogyo Kabushikikaisha, the name of the huge Japanese manufacturing company that produces roughly half of the world’s zippers. Founded by Tadao Yoshida in Tokyo in 1934, the company became a global zipper powerhouse, and its familiar YKK logo now appears on the pull tabs of zippers around the whole world.

Every time you receive an invitation to a wedding, birthday, or other important event, there it is: "RSVP" in all caps. But what do those four letters actually mean?

The initialism comes from the French phrase Répondez s'il vous plaît, meaning "please reply," or literally, "respond, if it pleases you." The request for a response originated in Europe and was adopted by the American elite, who embraced French court etiquette in the 18th century, preserving the French expression. Today, RSVP has become a practical yet elegant way to ask guests to confirm whether they’ll attend, helping hosts know how many people to expect.

One of the most famous codes in the world, SOS is the quintessential emergency signal, recognized across languages and around the globe. But what do those three letters actually mean?

Contrary to popular belief, SOS doesn’t stand for "Save Our Souls" or "Save Our Ship." That misconception took hold in the early 1910s and became widespread after the sinking of the Titanic in 1912. In reality, the letters don't stand for any words; the signal was chosen internationally at the Berlin Radio-Telegraphic Conference in 1906 and went into effect in 1908 because of its distinctive Morse code sequence. Three dots, three dashes, and three dots (... --- ...) create a simple rhythm that is easy to send and recognize during an emergency.

Have you ever noticed a strange "SSSS" code on your boarding pass? Perhaps you saw it the same day you were pulled aside for an extra security check before boarding. That’s no coincidence.

It stands for "Secondary Security Screening Selection". It’s a designation placed on some boarding passes by security authorities, such as the TSA, indicating that the passenger has been selected for additional screening, which can include a pat-down, baggage inspection, or explosive-residue swab. But seeing SSSS doesn’t necessarily mean there’s anything suspicious. Passengers can be selected based on certain travel or booking criteria, but they may also be chosen at random. If you see SSSS on your boarding pass, give yourself an extra 30 to 45 minutes, since the additional screening can take more time.

In countless history books, timelines, and educational materials, we see the abbreviations B.C. and A.D., or their modern alternatives, B.C.E. and C.E. But why do we use them, and why are there two versions?

We use these abbreviations to date historical events, counting years backward before the traditional birth of Jesus and forward after it. B.C. means "Before Christ," while A.D. stands for Anno Domini, a Latin phrase meaning "in the year of our Lord." The modern alternatives use more secular language: B.C.E. means "Before the Common Era," and C.E. means "Common Era." Both systems use the same year numbers and the same calendar points; the difference is simply whether the terminology has an explicitly Christian reference.

At the end of a U.S. mailing address, right after the city and state, we have the familiar ZIP Code. We’ve been using it for decades, but many people still don’t know exactly what those three letters stand for.

"ZIP" stands for "Zoning Improvement Plan." The U.S. Postal Service introduced the system in 1963 as mail volumes continued to rise, making faster, more efficient processing more and more important. These codes divided the country into geographic areas, giving postal workers a more organized way to sort and deliver mail. They also became an important part of the Postal Service’s growing use of automated sorting machines, helping mail literally "zip" through the system.

Have you noticed that whenever you forward an email, the abbreviations CC and BCC are right there? These familiar letters actually come from a time long before email.

CC stands for "Carbon Copy" and means other recipients can receive a copy while their addresses remain visible. BCC, or "Blind Carbon Copy," also sends a copy, but hides the recipient’s address from everyone else. The terms date back to the days of typewriters and carbon paper, which allowed people to make duplicate copies of a letter as they typed. A "CC" notation showed who else received a copy, while a "BCC", or blind copy, kept that additional recipient in secret.

"P.S." is undoubtedly one of the most familiar abbreviations used in letters and emails around the world. But do you know exactly what it means and why we use it?

Before computers and smartphones made it easy to edit text, writing a letter by hand meant that forgetting something often meant adding it afterward. "P.S." comes from the Latin post scriptum, meaning "written after." Adding it at the bottom of a letter gave you a simple way to include an extra thought or piece of information without rewriting the entire page.

You’ve probably used your debit card PIN countless times. Most people know theirs by heart, but how many of us actually know what those three letters stand for?

"PIN" stands for Personal Identification Number, a security code used to verify that the person using a card or accessing an account is authorized to do so. It dates back to 1966, when the PIN system was developed as part of efforts to create an automated cash dispenser. The following year, in 1967, the first ATM was introduced for public use. But there’s one small mistake many of us make without realizing it: "PIN number" is redundant, because the "N" already stands for "Number."

Whenever we read an explanation or definition, we often come across "e.g." and "i.e.", especially in dictionaries and reference books. They may look similar, but what do those letters actually stand for?

"E.g." is short for the Latin exempli gratia, meaning "for example." On the other hand, "i.e." comes from the Latin id est, meaning "that is" or "in other words." The two are easy to confuse, but they serve different purposes. Use "e.g." when you want to give a few examples of something, such as "I like tropical fruits, e.g., mangoes and pineapples." And "i.e." when you want to clarify or restate exactly what you mean, such as "I am a vegan, i.e., I do not eat any animal-based products."

Color me intrigued

Before the pantone: 10 color shades with old names

Colors come in a multitude of shades, most of them with a very specific name. Some of these names are a reference to a common object of that color —for example, ruby, maize, or lavender— while others, much more modern, are just a product of marketing, popular use, or just imagination —such as razzle dazzle rose, school bus yellow, or French blue. But some specific shade names have a story that goes back centuries, across different cultures and traditions. Here are ten color shades and the history behind their name.

This vibrant red-orange shade takes its name from an ancient pigment, highly toxic, made from cinnabar, a form of mercury. Its name comes from the Old French vermeillon, derived from vermiculus, a diminutive of the Latin vermis (‘worm’). What did this toxic pigment have to do with worms? An insect called Kermes vermilio was used to make a natural dye in a similar shade, but much more common than cinnabar, so its name became popular and was used for all similar red-orange shades.

Described as a shade that goes from light-brown to brownish-orange, tawny is associated with tanned leather, not only in color but in the origin of its name. Celts used tannum or crushed oak bark to treat animal hides and produce leather. Though Latin, this word made its way into Old French as tauné, ‘tan leather colored’, and then into English.

With a name that alludes to the sea, the origin of this deep blue shade seems to be quite straightforward, except it isn’t. Ultramarine blue takes its name from the Ultramarine pigment, made from grinding lapis lazuli stone. This pigment, as costly as gold, was imported from Afghanistan by Venetian merchants, who called it (azzurro) oltramarino or ‘(blue) from beyond the sea’.

Now described as cream or grayish yellow, ecru was initially used to describe the color of unbleached linen. Before bleached into a creamy white color, linen would retain the color of the dried flax fibers used to weave it. The French word écru, meaning ‘raw’ or ‘unbleached’, initially served as a mere descriptor of the fabric's state, but was eventually associated with its color.

To no one’s surprise, the name of this blueish-green shade comes from French. But although its French equivalent, vert-de-gris, means ‘green of gray’, there is no gray in its origin. There are two possible origins for this name: the first one is vert d'aigre or ‘green made with vinegar’, because a pigment of this name was made using copper and vinegar. The second one ties this shade to art objects imported from Greece, which gave way to the name vert-de-Grèce, ‘green of Greece’.

Indigo is used to describe a variety of blue shades, from the dark blue in the rainbow to various blue hues that can be achieved using indigo dye. Originally, the term indigo, from the Latin indicum (‘Indian’), was specifically used for a pigment made from the Indigofera plant and exported from India. Later on, the term became synonymous with the various blue shades resulting from that dye.

Nowadays, we automatically associate the color sepia with old photographs, but did you know its name and hue come from a fish? In ancient Greece and Rome, the ink of the sepia cuttlefish was used for writing, and it remained a commonly used drawing ink up until the early 19th century, when it started being used for watercolors and oil paints.

This one is tricky. As a color, auburn is a shade of brown, though it is often used to describe a specific type of red hair that has a mixture of red and brown tones. The term auburn, however, has nothing to do with red nor with brown. It comes from the French alborne, derived from the Latin alburnus or ‘off-white’, and it was used for blond people. How did it come to mean reddish-brown? Auburn and brown sounded similar.

Technically, there is no color named purpura in modern English, but there used to be. Made from crushed sea snails, the purpura dye was extremely expensive, and it became associated with royalty. Originally called porphura by the Greeks, the word was latinized as purpura, and was later adopted into English as purpul, from where we get the modern ‘purple’. So, while purpura is the original purple, it is nowadays called Tyrian or royal purple to avoid confusion.

This reddish-orange shade gets its name from the jasper, a semiprecious quartz known for having a pattern. The name ‘jasper’ comes from the Greek iaspis, meaning ‘spotted or speckled stone’. While there are multiple colors of jasper stones, the most common one is red, so the name of the stone became synonymous with that shade.