Oldenburg calls one's "first place" the home and those that one lives with. The "second place" is the workplace — where people may actually spend most of their time. Third places, then, are "anchors" of community life and facilitate and foster broader, more creative interaction.
Oldenburg suggests the following hallmarks of a true "third place":
Jeffres et al. (2009) listed the following types of environments as possible third places, considered in their research: community centers, senior centers, coffee shops and cafes, bars and pubs, restaurants, shopping centers, stores, malls, markets, hair salons, barber and beauty shops, recreation centers, YM/WCA, pools, movie theaters, churches, schools, colleges and universities, clubs and organizations, libraries, parks and other places allowing for outdoor recreation, streets, neighbors’ yards, homes and apartments, and events like neighborhood parties, block parties, cookouts, barbecues, town meetings, bingo, and various media (online, newsletters, newspapers, phone, bulletin boards).
The concept of a "third place" has become popularized and has been picked up by various small businesses, including as a name for various locally owned coffee shops, and is commonly cited in urban planning literature on the issue of community-oriented business development and public space.