It's possible that:
* It's a regional slang term: There might be a specific region or dialect where "mimis" has a particular meaning, but it wouldn't be understood by everyone.
* It's a misspelling: It's possible you're thinking of a different word that's been misspelled, such as "mimos" (meaning "mimes") or "mí mismo" (meaning "myself").
* It's a made-up word: Some people might invent words for fun or creative purposes.
To clarify the meaning, please provide more context. For example, where did you encounter this word? Was it in a conversation, a song, a book, or something else? This will help me understand the intended meaning and give you a more accurate answer.