1. A squeezing together; the exertion of pressure on a body in such a way as to tend to increase its density; the decrease in a dimension of a body under the action of two external forces directed toward one another in the same straight line.
The definition information for compression is provided by Stedman's. You can search our medical dictionary here.
Stedman's, part of Lippincott Williams & Wilkins, provides a comprehensive line of health-science publications for healthcare professionals and medical students.