The essence of meditation is training in mindfulness. This is done by resting the attention on an external meditation support, and returning to it every time it drifts away into thought. This action is possible because one part of the mind observes and identifies with thoughts and feelings as they arise. If we did not have this capacity for self-reflective awareness we would not know or realize we were thinking when thinking happens. We call the part of the mind that observes “observer consciousness” and the part that thinks and gets observed as “activity mind”

Rob Nairn, Diamond Mind: A Psychology of Meditation