An individual who chooses to live either on the streets or where ever she/he is at the moment. These people are often travelers (drifters); hippies who know that even though it is sometimes slightly uncomfortable you may live in Amerika without paying taxes and other advantages that are deemed natural; punks or even political refugees.
And it's totally free though illegal in most areas, so watch out for pigs that will want to hassel you. (You aren't human in Amerika unless you pay their taxes).
These punk squatters I once knew squatted because they were touring with bands 9 monthes out of the year. When not in a van going to the next city you can easily couch surf.