"street meme": a sticker, stencil, or poster that can spread a single image around the world. Unlike traditional graffiti art where each piece is unique, street memes can be copied repeatedly, taking on a life of their own, and spreading through the collective effort of people scattered around the world.

"meme": A term coined by Biologist Richard Dawkins to describe self replicating ideas. Read more about the concept of the meme here.