Original: Not wearing underwear under one's outer clothing is known in American slang as freeballing for men or freebuffing for women; in addition, the term going commando is used for both sexes.
Simplified: Not wearing undergarments under one's outer clothing is known in American slang as "freeballing" for men or "freebuffing" for women. The term "going commando" is also used at times, for both sexes.