Ad orientem: literally, "towards the East"
...When the priest is celebrating Mass, it is really a prayer to God. The priest at Mass most of the time is directly speaking to God. However, there are times in the Mass when the priest is directly speaking to the people and invites them to engage in a articular action like offer a sign of peace to each other. Those times when the priest addresses the people, he turns to face them, then turns to address God as he beings the prayer again. Why
Ad orientem is important then, is that it provides a great teachable experience to all regarding what is happening
theologically at Mass...