Like if you and a friend are annoyed at how someone else is acting and you want to talk about it, is that venting or gossiping? It's hard for me to tell the difference between making fun of someone and just getting your feelings out.
the way i see it you are venting if what you are saying is a hundred percent true gossiping is when you hear things from somebody and you have no way of determing whether it is true and you pass this on to somebody else who in turn will repeat it again to another person and so it goes on