So I've just learned about this word/concept and it's been making me stagger a bit.
It's Greek in origin, and the Greek word means something like 'having a goal' or 'creating completion'
Aristotle uses it when talking about plants and seeds. It's the essence of what's in a seed that makes it grow into the right kind of plant - the essential thing that makes a tomato seed grow a tomato plant or a pumpkin seed a pumpkin vine. In other words, the entelechy of the acorn is an oak tree, the entelechy of a caterpillar is a butterfly and so on.
It's a fantastic word that holds in it the concepts of soul, potential, growth, transformation, self-actualization, possibility. It's a way to name one's purpose and reason for being.
What kind of oak tree is already there, waiting for me to manifest it?