I couldn’t do any better than quote from Richard Dawkin’s book – The God Delusion.
“Let’s remind ourselves of the terminology. A theist believes in a supernatural intelligence who, in addition to his main work of creating the universe in the first place, is still around to oversee and influence the subsequent fate of his initial creation. In many theistic belief systems, the deity is intimately involved in human affairs. He answers prayers; forgives or punishes sins; intervenes in the world by performing miracles; frets about good and bad deeds, and knows when we do them (or even think of doing them). A deist, too, believes in a supernatural intelligence, but one whose activities were confined to setting up the laws that govern the universe in the first place. The deist God never intervenes thereafter, and certainly has no specific interest in human affairs. Pantheists don’t believe in a supernatural God at all, but use the word God as a nonsupernatural synonym for Nature, or for the Universe, or for the lawfulness that governs its workings.
Deists differ from theists in that their God does not answer prayers, is not interested in sins or confessions, does not read our thoughts and does not intervene with capricious miracles. Deists differ from pantheists in that the deist God is some kind of cosmic intelligence, rather than the pantheist’s metaphoric or poetic synonym for the laws of the universe. Pantheism is sexed-up atheism. Deism is watered-down theism.”
As far as defining atheism goes – here’s Wikipedia’s stab at it is this -
“Atheism, as a philosophical view, is the position that either affirms the nonexistence of gods or rejects theism.
When defined more broadly, atheism is the absence of belief in deities, alternatively called nontheism.”