means friend of a friend.
This is such a loaded expression. It starts with "friend". Not a formal relationship, but a tenuous one. And a relationship that doesn't belong to you! The friendship is between your friend and her friend.
The very idea of utilizing a FOAF network for your own gain is scary. Scarier still is allowing your FOAF network to be used by someone else to make a profit.
There are firms sprouting up every day promising big companies that they will do just that. That they'll organize and exploit FOAF networks to product big profits for corporations. It might work for a little while, but not for long.
The reason is the tenuous nature of the friendships. The fourth person in the chain (marketer, you, your friend, your friend's friend) is awfully low on the totem pole.
So what works? Two things:
1. Smooth, simplify and formalize the process of spreading the idea so if an idea is worth spreading, it'll run into less friction. The white headphones on the iPod, for example, amplify the message of the player even when someone can't see it.
2. Make stuff that people want to spread even if they don't care about you. The Republicans definitely got this right during the last election cycle.