Graffiti (singular: graffito; the plural is used as a mass noun) is the name for images or lettering scratched, scrawled, painted or marked in any manner on property. Graffiti is sometimes regarded as a form of art and other times regarded as unsightly damage or unwanted.
Graffiti has existed since ancient times, with examples going back to Ancient Greece and the Roman Empire and may range from simple scratch marks to elaborate wall paintings. In modern times, spray paint and markers have become the most commonly used materials. In most countries, defacing property with graffiti without the property owner's consent is considered vandalism, which is punishable by law. Sometimes graffiti is employed to communicate social and political messages. To some, it is an art form worthy of display in galleries and exhibitions, to others it is merely vandalism. There are many different types and styles of graffiti and it is a rapidly evolving artform whose value is highly contested, being reviled by many authorities while also subject to protection, sometimes within the same jurisdiction.
source : wikipedia