Agnosticism is a philosophical position that the existence of God is not knowable. The word “agnosticism” comes from the Greek, a meaning without, and gnosis, meaning knowledge. It literally means "without knowledge" but is usually applied to the topic of God.
Agnosticism is really a subdivision of atheism. Since atheism denies the existence of God, agnosticism does the same thing by not affirming God's existence.
Weak agnosticism says that God is simply not known if he exists at all. Strong agnosticism says that God cannot be known.