The three terms are related, but mean three different things.
Atheist: anyone that lacks belief in deities.
Anti-Theist: anyone that is opposed to religion and/or the religious.
Agnostic: anyone that claims to lack knowledge one way or the other, usually used in conjunction with the existence of deities.
Atheist: anyone that lacks belief in deities.
Anti-Theist: anyone that is opposed to religion and/or the religious.
Agnostic: anyone that claims to lack knowledge one way or the other, usually used in conjunction with the existence of deities.