The models installed a webcam on their computer so that you can see them live.This video is instantly (with no delay) broadcasted to you.You can watch the model and the model can see you (if you have a webcam installed).
This is a much more real life experience than chatting with a keyboard in a chatroom.
Only private cam sites allow you to broadcast yourself to the cam model.
Cam2Cam means during a webcam chat session, it's not just the viewer can see the chathost/performer but the performer can see the viewer too.
Cam2Cam becomes more popular when a few big webcam sites like i Friends and im Live start to implement it.
This because there is a human interaction between you and the model.