Commando is the state of not wearing underpants. Typically a person is said to “go commando” if they don’t wear underpants underneath their clothing.
Certain clothes are designed for going commando, like kilts, sarongs, and swimwear. However, people can go commando wearing any clothes they like. It may be uncomfortable in very tight-fitting clothes, like skinny jeans, though.
While the origins of the term are unclear, commandos are military soldiers or units. The phrase “going commando” may refer to the genitals being like soldiers, “out in the open” or “ready for action.”
Both men and women can go commando. Free balling (for men) and free buffing (for women) are two gender-specific synonyms for going commando.