Black Day (April 14) is an informal tradition for single people (a.k.a. Unit Solo, Korean: 솔로부대) to get together and eat noodles with black bean sauce in South Korea, sometimes a white sauce is mixed because those celebrating the Black Day didn't experience the White Day.

The idea is that those who didn't give or receive gifts on Valentine's Day or White Day can get together and eat Jjajangmyeon (짜장면), white Korean noodles with black bean sauce (hence the name), to commiserate their singledom.