The most common kinds of Peer Review are peer observation of teaching and peer appraisal.
Peer Observation of Teaching is a method for gaining feedback on your teaching. It involves a colleague sitting in on a teaching session and afterwards offering constructive comments on what you are doing well and what you might do to improve. Feedback is generally structured around a teaching observation proforma, of which there are many different examples. Feedback is generally discussed in a post-observation meeting and it may also be written up on the teaching observation proforma. This is often the case if the observation is being used as evidence on which a performance judgment is being made.
Peer observation of teaching can be undertaken as a reciprocal arrangement if the teaching observation is for developmental purposes. This enables you to evaluate another person's approach to learning and teaching and hopefully gather ideas to help you enhance your own teaching practice.
Peer Appraisal is a method for gaining feedback, often in relation to leadership or management skills but potentially in relation to teaching, in a team-teaching situation.
Again it involves eliciting feedback, often structured around a series of questions or themes.