Actualization is making a plan, a wish, or a possibility become real — not staying in the head, but showing up in the world. It is a formal, rather heavy noun. Psychology and self-help use it a lot; the famous phrase is self-actualization, becoming the person you have it in you to be. In ordinary talk, most people would just say making it happen or carrying out a plan. You will meet actualization in essays, coaching, and business-speak (the actualization of the strategy). British spelling often uses s: actualisation. Same word.