1. In a state of secrecy or minimal public knowledge; being known only by a select few people. Keep this on the down low, but Janet is planning to break up with Kevin next week. My parents know about the pregnancy, but I'd like it to stay on the down low otherwise.

2. In a state of secrecy or minimal public knowledge pertaining to the activities of a man who has sex with other men but considers himself to be heterosexual. I never thought he was gay, but then I started to hear rumors that he's on the down low.