The term, 'Public Art' probably best captures what the artists intension and community receipt of this art type is.  Other names for it are street art, graffiti, tagging, community service... Public art is one of my favorite genres, not just because it's free to go see, but it comes up on you and enhances your day when you weren't expecting it. One of the reasons I went into Interior Architecture was to affect peoples' experience of day to day activites; public artists have passed, considered, and reconsidered the location they choose, then address it with the content they think most appropriate. It is the most site-specific fine arts genre, and the cultural impact is outstanding. Here are a few that I admire:
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By Tilt in Marceille, France. Reposted from Post + Grant.

By SoulKontroll in Well Fleet, MA.

By Unknown in NYC. From FreshPaintNYC.

By Unknown on Fillmore & Laussat in San Francisco.