Graffiti
Writing or drawings scribbled, scratched, or sprayed illicitly on a wall or other surface in a public place, ( The Oxford English Dictonary )
Art
The expression or application of human creative skill and imagination, typically in a visual form such as painting or sculpture, producing works to be appreciated primarily for their beauty or emotional power, ( The Oxford English Dictonary )
I think that it can be both because if it is on a wall or someone has been payed to spray paint it then it is art because it’s not illegal and there doing a job, but then I think it could be vandalism because if it is on a gravestone or car and it has a bad meaning or something bad on it, it is vandalism because they haven't been told to do it they just did it for fun.