The February 13 holiday celebrating female friendships, popularized by Parks and Recreation, is Galentine’s Day.
Galentine’s Day was created for the sitcom’s character Leslie Knope, played by Amy Poehler. In the show, Leslie gathers her female friends for a pre-Valentine’s celebration centered on friendship, appreciation and a breakfast-style get-together. The name combines “gal” with “Valentine’s,” making the purpose clear.
The holiday appeared in the season-two episode “Galentine’s Day,” which first aired in 2010. Although it began as a fictional tradition in the NBC comedy, the idea moved beyond the show through social media, press coverage and real-world brunches, parties and friendship-themed events.
February 13 is the traditional date because it falls immediately before Valentine’s Day, but Galentine’s celebrations are not official public holidays and can be held whenever friends are available. The original concept focuses on women celebrating women, while modern usage is sometimes broader. “Palentine’s Day” is a related adaptation for friendship more generally, but it is not the canonical answer to this question.