Here are the correct definitions.
Atheist = Someone that does not believe that god(s) exist.
Theist = Someone that does believe that god(s) exist.
Agnostic = Someone that believes that no one can know whether or not god(s) exist.
Atheist = Someone that does not believe that god(s) exist.
Theist = Someone that does believe that god(s) exist.
Agnostic = Someone that believes that no one can know whether or not god(s) exist.