Washrooms have many names around the world, but one abbreviation appears frequently across the UK and Europe: “WC.” Seen on signs in airports, hotels, restaurants, and train stations, the letters stand for “Water Closet,” an old term for a small private room containing a toilet connected to a water supply.

The expression dates back to the development of indoor plumbing in the 19th century. Before then, bathrooms were mainly associated with bathing, while toilets were often located separately. As flush toilets became more common indoors, compact rooms designed specifically for them became known as water closets.

Although modern bathrooms are very different from those early spaces, the abbreviation “WC” has remained widely used, particularly in Europe. For many people, it is simply a familiar part of everyday life and travel, while others have encountered the signs for years without knowing exactly what the letters mean.

The story of “WC” is a small example of how language can preserve traces of older technology and architecture. So the next time you see those two letters on a door, you’ll know that they are short for “Water Closet”—a term that has survived long after the original concept became part of modern bathroom design.