Gossip is sharing private information with those who are not part of the problem or part of the solution.
When we speak things about others that we would be ashemed to say in their presence, we are not only disobeying God's Word(Lev. 19:16), we are also destroying that person's reputation in the mind of our listener. Scripture states the sin of gossip is not limited to the spreading of lies alone, but also to the improper involvement of yourself in another's personal business(tim. 5:13). Even to participate in the act of gossip as a listner is a sin(Prov.20:19). In willfully listening to the one who gossips, we sanction the destruction of the other person's reputation.