What is "co-training"?

As per this paper : Co-training like self-training learns on its own predictions. However, co-training learns two separate models (which are assumed to be independent typically by training on disjoint feature sets). These models are applied to unlabeled data. Examples on which these two models agree are treated as labeled data for a new round of training. One could incorporate model confidence to include only examples both models are confident of.
The definitive paper is Blum and Mitchel
Also this paper by Collins and Singer.