down low

Short definition from Wiktionary

Noun

1. 1
   A state of secrecy.
2. 2
   The state of being a man who secretly sleeps with people other than his partner.
3. 3
   The state of being a man who secretly sleeps with other men.
4. 4
   A man who secretly sleeps with other men.
5. 5
   Alternative spelling of down low.

Adjective

1. 1
   Undercover or lying about one's identity.
2. 2
   Purporting to be heterosexual while engaged in sex with men.