Body odor: An unpleasant smell produced after perspiration. Body odor occurs when sweat contacts bacteria that normally reside on the skin. Sweat itself is almost odorless, but the combination of sweat with skin bacteria can produce an offensive odor. Good hygiene and antiperspirant or deodorant products can be used to manage the condition. In some unusually severe cases, prescription strength deodorants or antiperspirants may be required. Also known as "B.O."