Why do we call it "Relaxation"?
There are many techniques of relaxation being taught in a variety of contexts, including for physical health, stress management, psychological inquiry, as well as spiritual purposes. Many of these methods are extremely useful and serve their practitioners well.
However, here we are addressing Yoga Meditation, which is a process of knowing ourselves at all levels, such that we may eventually come to experience ourselves at the deepest level, the center of consciousness that goes by many names.
It is a process of surveying inside: It has become common to refer to the surveying of the body and other internal states as a practice of relaxation. Actually, it is more accurate to call it surveying than relaxation, since the actual activity being performed is surveying. Some schools of meditation put their main emphasis on such practice.
The practices in Yoga are not merely means of inducing relaxation through an external stimulus or creating internal fantasies, though they are definitely relaxing. Rather, it is a process of surveying, introspecting, or exploring.