Bio-Ogranic Weapons (B.O.W.s) are products of the T-Virus created by the Umbrella Corporation. Keep in mind that a B.O.W. is a creature deliberately administered the T-Virus, rather than a creature that accidentally contracted it or a creature that is not effective as a weapon (i.e. A Cerberus is a B.O.W. A Zombie is not. The Tyrant is a B.O.W. Lisa Trevor is not.).
List of B.O.W.s (B.O.W. No., if applicable)
Hunter Alpha (MA-121α)
Hunter Beta (MA-121β)
Hunter Gamma (MA-124γ)
"Mr. X" (T-103)