The main difference is in your motivation. A compulsion is anything you say or do to relieve your anxiety. They can be physical (handwashing, tapping, checking, counting, searching on Google) or mental (avoidance, what ifs, rumination, replaying something you did or said over and over again in your mind, imagining the worst case scenario, trying to replace the intrusive thought with a positive, distracting yourself, trying to reason or argue with the intrusive thought. Trying to convince yourself the intrusive thought isn't true. Even something like prayer can be a compulsion. Doing a compulsion DOES relieve your anxiety, but its very short lived.