Coveillance is peer-to-peer surveillance (Rainie & Wellman, 2012, p. 233) where people observe each other. Looking an old friend up on Facebook to see what they are up to is an example of coveillance (p. 238). Other examples are researching service providers, looking for family members, neighbors, or coworkers, personal searches looking up information on adopted parents, looking at the criminal records of friends or other acquaintances, or online dating sites (p. 239). Watching others allows insight into "political views, the cultural tastes, the friendship circles, the basic lifestyle preferences, and even the daily activities of those in their networks" (p. 240).
References:
Rainie, H. & Wellman, B. (2012). Networked: The New Social Operating System. Cambridge: MIT.