A trigger point is a muscle knot. These are the painful dull achey spots that you get in your muscles that often refer pain to other places. For instance, a lot of tension headaches are cause by trigger points in your shoulders and neck. Effective trigger point therapy requires a detailed knowledge of anatomy and great problem solving / detective work skills. It is really one of my favourite areas in massage and can be wildly effective in reducing pain, reducing anxiety, improving muscle health and function and promoting overall well being.