A social exchange network is either a website or app that allows people to sign up and exchange different social media interactions with other users.
For example one user may have a facebook page that they want people to like. They can share their page on the social exchange network and receive new likes to their page if they perform enough social media interactions with other users on the social exchange network.
It's a way of receiving social media interactions on your accounts in return for performing interactions on others accounts.
However on these social exchange networks you must perform more interactions than you receive so that the exchange network always has an excess of interactions that they can use to run paid promotions for services such as Instant Views.