Follows same definition as cum_on_clothing:

"This tag is used when there is cum visible on the clothing of a character."

Could apply to the following:
(1) depiction of a character wearing panties with cum (usually from an external origin) on its outward facing side, and/or

(2) same as the previous but with cum on any part of the panty from an external origin (e.g. lowered panties with cum dripping down onto it) or cum explicitly depicted to have been done upon by another character, or

(3) cumming on unworn panties

See Also

• cum_in_panties
• cum_on_underwear