You probably have seen people using LMK and you wondered what exactly it might mean. LMK is an acronym for 'Let Me Know'. The expression is mostly used when people want to add information about something you are discussing, they will you Lmk, meaning they want more gist about the topic of discussion.
Lmk is used mostly by adults and younger ones who are users of any of the available message apps. It is often by people when chatting. But one should be careful not to be using it in formal writing or discussion. Typing lmk saves time, energy than writing it in full.
You can use lmk in the beginning, anywhere in the middle or at the end of a sentence. It can also stand alone but like I said earlier, if the communication you are having is quite a formal one, don’t dare use LMK.