Graffiti: The word first appeared in print in 1851, describing ancient wall inscriptions found in the ruins of Pompeii. It is from Italian; "graffiti", plural of "graffito" and means literally - "a scribbling."
This is, in turn, derivative formation from 'graffio' - "a scratch or scribble," and from 'graffiare' ; "to scribble." The sense of the word was extended in 1877 to include 'recently made crude drawings and scribbling'.
Dictionaries are now recognizing that 'graffiti' is often used in the singular, as in "the graffiti is...", although they are still casting a jaundiced eye on such usage.
The simplest and most generally accepted meaning today for Graffiti is:
"An unauthorized, often illegal drawing or writing,
either in a public place or that can be viewed from a public place - such as on a wall or bus - generally using spray paint."