Being able to do as one pleases; free to control or handle something at will (often used as '自在に～する').
彼はパソコンを自在に操ることができる。
He can operate computers with ease.
習熟すれば道具を自在に扱えるようになる。
With practice you'll be able to handle the tools freely.
想像力が自在に働く環境を作りたい。
I want to create an environment where imagination can work freely.
An abbreviation of '自在鉤' — a hook used to hang pots; a specialized/historical term not common in everyday speech.
古民家の囲炉裏には昔の自在が残っていた。
An old hook (jizai) remained at the hearth of the old folk house.