What does nmu mean in slang?

"NMU" is not a widely recognized slang abbreviation. It's possible that it's a specific term used within a particular group or community.

If you can provide more context about where you encountered this abbreviation, I might be able to give you a more accurate answer.

For example:

* Where did you see it? (e.g., online, in a conversation, etc.)

* Who was using it? (e.g., friends, family, online community, etc.)

* What was the surrounding context? (e.g., what were they talking about?)

With more information, I might be able to decipher its meaning.