Expansion means opening up and making room for difficult feelings, urges, and sensations, thereby allowing them to "flow through" you without a struggle. You don't have to like or want these feelings; you just make room for them and allow them to be there even through they are unpleasant. Once you learn this skills, if these feelings resurface, you have the tools to make room for them and let them "flow on by" so you can invest your time and energy in doing meaningful life-enhancing activities instead of struggling. Aim to practice on a daily basis.
Developed from Russ Harris - ACT Made Simple - Acceptance and Commitment Therapy.