Friending is the act of adding someone to a list of "friends" on a social networking service. The notion does not necessarily involve the concept of friendship. It is also distinct from the idea of a "fan" — as employed on the WWW sites of businesses, bands, artists, and others — since it is more than a one-way relationship. A "fan" only receives things. A "friend" can communicate back to the person friending.
The act of "friending" someone usually grants that person special privileges (on the service) with respect to onesself. On Facebook, for example, one's "friends" have the privilege of viewing and posting to one's "wall".
Read more about Friending: Friend Collecting, Social Network Friending and Friendship, Ethical Considerations