Atheism is a rejection, non-acceptance, or indifference to theism, which boiled down to its essence is just a non-acceptance of deities being the creator or essence of reality. One can be atheist and hold hard-line rationalist views about the nature of reality, but one can also have spiritual beliefs and be atheist.

Agnostics believe that in some way, metaphysical intelligences are involved in the creation or fabric of the universe, but the very nature and depth of this involvement is in varying degrees indecipherable, unknown, and not-yet-known. Agnosticism doesn't require either the acceptance or rejection of theism.

Put together it technically means the person doesn't believe in a theistic god but holds agnostic views about broader metaphysical concepts.

More colloquially I've noticed a lot of people use the atheist agnostic / agnostic label interchangeably to indicate they haven't made their mind up one way or the other, but it's possible to be either atheist agnostic or theist agnostic.