down low, n. — Green’s Dictionary of Slang

down low n.

1. (US black) a state of secrecy; usu. in on the down low

2002

(con. 1998–2000) J. Lerner You Got Nothing Coming 99: Tells me to ‘keep it on the D.L.’ ‘What’s the D.L., Skell?’ [...] ‘The D.L., dawg, is the down-low. You keep something on the D.L. and it stays with you — you down wid that?’.

2. (US black) ostensibly heterosexual, married men who enjoy sex with homosexual men.

2005		N.Y. Blade 27 May 🌐 While no one tried to dismiss the reality of the down low, everyone on the panel wondered why the ‘DL’ eclipsed all other issues and concerns when the conversation turned to sexuality, increasing HIV rates, and the black community.
2005		talesofthesissy.blogspot.com 20 Apr. [blog] There’s this thing with men [...] down low, or low down... down low guys – [...] these are men who are married and have children – they love their families and want to stay with them, but they have anal sex with other men.

In phrases

on the down low (also on the d.l./low)(orig. US black)

1. in the background; in a clandestine manner.

1992		UGK ‘Cocaine in the Back of the Ride’ 🎵 On the low my fuckin momma knows.
1996		Eble Campus Sl. Mar. 3: the d.l. – secret: ‘I’ll tell you about Mike if you keep it on the D.L.’.
1997		‘Q’ Deadmeat 215: How about talking to him on the downlow.
2000		hipslang.com 🌐 We movin’ on up to the east side, big pimpin, bling-blingin’ and shit. and soon yall fools will be able to see profiles for the boyz behind tha slang! Keep it on the DL.
2003		G. Tate Midnight Lightning 27: Other Black performers went to keep their liaisons with white women on the downlow back then.
2003		Eble Campus Sl. Nov. 5: on the d.l. – in secret.
2004		Mad mag. June 16: Will you guys promise to keep it on the down-low?
2011		G. Hayward Corruption Officer [ebk] cap. 18: Every time they want to handle an inmate and keep it on the low, these Supervisors are going to be asking you to take a walk with them.
2017		T. Pluck Bad Boy Boogie [ebook] ‘Dante’s got his nose open for her [...] But keep that on the DL’.
2018		Unknown T ‘Mad about Bars’ 🎵 I done so much work on the low / I’m only young, mixing a pyrex bowl.
2019		S.M. Jones Lives Laid Away [ebook] ‘Got it on the down low that you was heading to that recording studio’.
2020		G. Armstrong Young Team 8: He wears the clothes n walks the walk but he keeps it on the doon-low really.
2021		S.A. Crosby Razorblade Tears 124: ‘Lots of folks still bere on the down-low’.

2. of a (married) man, having homosexual relations despite parading an ostensibly heterosexual lifestyle.

2000		Blackboiz for Other Boiz 🌐 12 Jan. I am str8acting and on the DL. I am look for the same.
2002		ADS-L 6 May 🌐 The expression ‘on the down low’ today — in some circles — has an additional connotation of describing an African-American male who has sex with other men on the side but who would not necessarily describe himself as homosexual. ‘Keeping it on the down low...’ ‘DL Brotha.’.
2007		W.D. Myers ‘what would jesus do?’ inWhat They Found 18: ‘So I had to ask Evelyn did she ever think that maybe the brother [a single male courting Evelyn] is on the down low? Sneaking around and seeing men and stuff like that?’.

3. being a fan of hip-hop/rap music.

2002

ADS-L 6 May 🌐 ‘On the d.l.’ is common [...] hip-hop slang. It may or may not have started in prisons. It is not really accurate to describe it as African American because it’s kinda ‘postracial’ [...] in the sense that hiphop is. It’s used by Latinos, Whites and Caribbeans ‘who are down with hip-hop’ much as by African Americans, and I think it is pretty much avoided by African Americans.