You’ve probably seen the letters “WC” on restroom doors, especially while traveling, but do you know what they actually stand for? The abbreviation means “water closet,” an old expression referring to a small private room containing a toilet. While the phrase sounds unusual today, WC remains a familiar and widely understood label in many parts of Europe.

The term has a fascinating connection to the development of the modern flush toilet. In 1596, English inventor Sir John Harington described an early flushing toilet that used water to carry away waste. Nearly two centuries later, in 1775, Alexander Cumming patented an improved design featuring an S-shaped water trap, which helped prevent unpleasant sewer gases from traveling back into buildings.

As indoor plumbing became increasingly common during the 19th century, “water closet” became a practical term for a room containing a toilet. Over time, the two words were shortened to the simple abbreviation WC. It was compact, easy to display on signs, and could be understood even when people didn’t speak the local language.

The terminology eventually developed differently around the world. In the United States, people generally became more accustomed to terms such as “bathroom” and “restroom.” Meanwhile, WC remained common throughout many European countries and other parts of the world. That’s why some travelers may encounter the abbreviation frequently when visiting Europe, even if they rarely see it at home.

So the next time you walk past a door marked WC, you’ll know there’s a little piece of history behind those two letters. What began as the phrase “water closet” has survived for generations and evolved into a simple international abbreviation for one of the most familiar facilities in modern life.