According to Wikipedia, contemporary art is art produced at the present period in time. Contemporary art includes, and develops from, Postmodern art, which is itself a successor to Modern art. In vernacular English, "modern" and "contemporary" are synonyms, resulting in some conflation of the terms "modern art" and "contemporary art" by non-specialists.
Inside contemporary art, wikipedia defines street art as visual art created in public locations, usually unsanctioned artwork executed outside of the context of traditional art venues. The term gained popularity during the graffiti art boom of the early 1980s and continues to be applied to subsequent incarnations. Stencil graffiti, wheatpasted poster art or sticker art, and street installation or sculpture are common forms of modern street art. Video projection, yarn bombing and Lock On sculpture became popularized at the turn of the 21st century.
The terms "urban art", "guerrilla art", "post-graffiti" and "neo-graffiti" are also sometimes used when referring to artwork created in these contexts. Traditional spray-painted graffiti artwork itself is often included in this category, excluding territorial graffiti or pure vandalism.
Artists who choose the streets as their gallery are often doing so from a preference to communicate directly with the public at large, free from perceived confines of the formal art world. Street artists sometimes present socially relevant content infused with esthetic value, to attract attention to a cause or as a form of "art provocation".
Street artists often travel between countries to spread their designs. Some artists have gained cult-followings, media and art world attention, and have gone on to work commercially in the styles which made their work known on the streets.
Mixing medias, presenting the world with the eye of a photographer, a painter, reusing experiences to present a colorful artwork !