1. an adventure characterized by manliness or extreme masculinity.
2. an epic journey only undertaken by men, or very masculine women.
3. a strenuous task which only individuals naturally equipped with a legitimate, large penis can endure.
"Nah, not Alfred. He's too much of a pansy."
Man: Oh nothing, just the MANventure.
*Woman makes sandwich*
b. Any trip that deviates from the original plans and leaves the women-folk behind