It simply means "let me know." Or get back to me with answer.

If it already formally exists, I don't know, but I started using it in my e-mails in the '90s for convenience. Today, someone responded "OH!!!!!!" after I replied to his "what's the meaning of that" e-mail. So, there you have it.
In e-mail commonly, consider for example:
1) If you need anything, LMK.
2) What're you guys doing tonight? LMK.
by Lee Djangmah April 03, 2006
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(V.) LMK= let me know. Or, tell me pretty much right away what your response is so something actually happens.
*concert is tomorrow*
Me: Hey want to go to the concert tomorrow?
Friend: idk maybe, I have to ask
Me: ok lmk
by Stoinkydoinkycheese May 17, 2017
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Means Lick My Kitten, Kitten being slang for the female genetalia, this term would be used in the same context by a female that a male world use the phrase "Suck my dick" in
Girl: LMK
Guy: what's that mean
Girl: lick my kitten
by Random739104638 July 16, 2012
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1. Let Me Know
2. Lick My Knuts
"Just LMK if I can help you out"
"Just LMK if that will help"
by Anonymous September 30, 2003
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