JBJ originally stood for 정말 바람직한 조합 in Korean, meaning "A Really Desirable Combination." Later on, it also came to stand for Just Be Joyful.
JBJ was a fan-made project boy group made up of 6 trainees eliminated in the third round of eliminations in Produce 101 Season 2. The members were (and are) good friends, and fans liked their interactions both during and following the end of Produce.