Trigger point is a particular type of massage where extreme pressure is placed on a single clump of muscle tissue, usually where a knot is present. By applying 1-2 minutes of pressure, the knot relaxes, allowing blood to flow into the muscle tissue again.
The muscle fibers always want to move indepedently. A “knot” is a group of muscles that have been knotted together, either by simultanous contraction or scar tissue. Although trigger point massage is a very common practice, it is better known by clients of massage than by doctors in the field of medicine.
For more info, see the wikipedia page (embed that?)
