Graffiti is writing or drawing on walls, buildings, or other surfaces in public places, usually without permission.

When you see spray-painted words or images on a subway car or the side of a building, that's graffiti. Some graffiti is just a person's nickname or tag, while other pieces are elaborate artworks with multiple colors and complex designs. Graffiti artists, sometimes called writers, often work at night to avoid being caught, since most graffiti is illegal.

The word carries different meanings depending on who's using it. Property owners often see graffiti as vandalism, damage that costs time and money to remove. But some people view certain graffiti as genuine art that brings color and creativity to dull spaces. Cities sometimes set aside legal walls where artists can paint without breaking the law. A few graffiti artists have become famous, with their work appearing in museums and galleries.

Ancient Romans scratched graffiti into the walls of Pompeii nearly 2,000 years ago, and people have been leaving their marks on walls ever since. Whether you consider it art or vandalism often depends on the quality of the work, where it appears, and whether the property owner gave permission.