Graffiti is a term that is generally used to refer to text or images that are painted onto walls and buildings, usually with spray paint. When you think of graffiti, you probably think the art that you see on the street, the ones that you walk past every day.
Graffiti painting on walls and buildings is often done by unknown artists using bright colors, and they usually have written texts or slogans that go along with the image. It certainly has a very urban and modern connotation to it, and it is highly appreciated among the younger generations.