Deism is “belief in the existence of a supreme being, specifically of a creator who does not intervene in the universe” (Oxford English Dictionary).
Theism is “belief in the existence of a god or gods, especially belief in one god as creator of the universe, intervening in it and sustaining a personal relation to his creatures” (Oxford English Dictionary).
Look at the definitions. Deism describes a God “who does not intervene,” while Theism describes a God “who intervenes” in the universe. The single defining difference between Deism and Theism is whether God intervenes or does not intervene.
