A B.O.W(Biological Organic Weapon) is usually a geneticly engineered creature, such as a Hunter or a Cerberi. B.O.W's are not to be confused with Tyrants, whom are transformed humans who were capable of recieving the positive effects from the T-Virus but keeping thier humanity intact. However, they were still largely vulnerable to conventional attacks, and were deeply engineered, making them tougher and strong.
The only non-engineered B.O.W currently is the Licker, which is the third proccess in evolution from a Zombie. Once a Zombie has sustained enough blood loss through damage, they will continue to mutate into a Crimson Head, which has similar features to a Zombie, however they have elongated claws, deep red skin, and a ferocious instinctal nature and speed. Once a Crimson Head has sustained enough damage it will voilently mutate into a Licker, extreme heat however will halt this process.
If a Zombie or Crimson head is burnt or sustains damage to its brain it will not be able to continue its path in evolution.