I would suggest the overlap between Facebook and G+ is a reasonable definition for broad real life social network for communicating with real world fiends, family, and social activities. LinkedIn, Patron, Reddit etc have related features but are designed for different kinds of relationships and types of communication.

Arguably Instagram in April, 2012 was a reasonable pens vs pencil division where the courts could have included or excluded them quite reasonably. Though allowing Facebook to buy them suggest a vary narrow definition at the time.