Aristotle also pretty much invented modern logic. Except for its symbolic form, it is essentially the same today. What Plato called idea or ideal, Aristotle called essence, and its opposite, he referred to as matter. Matter is without shape or form or purpose. It is just stuff.
Essence is what provides the shape or form or purpose to matter.
Essence is perfect, complete, but it has no substance, no solidity. This process, the movement from formless stuff to complete being, is called entelechy, which some translate as actualization. There are four causes that contribute to the movement of entelechy. The thing s matter or substance. The metal, what it is made of.