What is the meaning of Mmm?

ISO 639-3 language code for Maii.

Symbol for micromillimetre , an SI unit of length equal to 10 millimetres .

An emotional expression of satisfaction.

An expression used to show thought, reflection, or confusion.

Used to represent an utterance that is muffled or spoken with a full mouth (also spelled "mmph").

Yes.

Used to signify that one is listening and understands

alternative form of hm

Source: wiktionary.org