Short answers, pulled from the story.
Public art is art in any media whose form, function, and meaning are created for the general public through a public process. It must be visually and physically accessible, installed in public spaces, and produced through official public processes of creation, procurement, and maintenance. Works that lack public sanction, such as unauthorized graffiti, generally fall outside the genre.
In the United States, public art is protected by the Visual Artists Rights Act of 1990, known as VARA. Unlike gallery, studio, or museum artworks, which can be transferred or sold freely, public art requires an official deaccession process before it can be sold or removed.
New genre public art is defined by Suzanne Lacy as socially engaged, interactive art for diverse audiences with connections to identity politics and social activism. The term emerged in the 1990s among artists who wanted public art to explicitly empower marginalized groups rather than merely reflect social issues through metaphor.
Richard Serra's Tilted Arc was removed from Foley Square in New York City in 1989 after office workers complained that the minimalist piece disrupted their work routine. A public court hearing ruled against the continued display of the work.
Maurice Agis' Dreamspace V, a large inflatable maze erected in Chester-le-Street, County Durham, killed two women and seriously injured a three-year-old girl in 2006. A strong wind broke its moorings and lifted it 30 feet into the air with thirty people trapped inside.
Agnes Denes planted a two-acre field of wheat in downtown Manhattan in 1982 with her project Wheatfield - A Confrontation. In the same year, Joseph Beuys began planting 7,000 oaks paired with basalt blocks in Kassel, Germany, with his project 7000 Oaks. Both works used ecological action as a form of public art to raise awareness of green urban design.