“On the low” or “Down Low” (DL) is a sexualized slang term that refers to men who identify as straight but have sexual/romantic relationships with other men. The term is used to avoid the homosexual identification, I would assume specially if they have female partners that they have not revealed to, or choose to not inform anyone else of their prefrences. The term is also used as a way to keep something a secrete or keeping it private.