To describe a loved one in which you are having an intimate relationship with.
The word moo is used to describe how beautiful,
gorgeous,
sweet,amazing, loving, caring, generous,lovely,funny,
sweet ect a person is.
If you cant think off the top of your head or can't be arsed to think of a good word to say just call them a moo and they can interprete what you mean. everybodys happy!
Also moo can be developed into moomin and mooie.