The word "mmmm" is a simple way of expressing enjoyment or satisfaction. It is often used when something tastes good or when we find something pleasant. Full definition
I have big boob love when a girl eat me n fuck me with a stripped on mmmm love it so much so want to fuck me at melrose park il (nsalesbians.com)
Five minutes into the hideous procedure, a courier arrived with a parcel and she had to «mmm mmmm glmm mmm» her way through receiving it, leading him to think she has some sort of affliction and nervously ask «Is anyone looking after you, love?» (housegoeshome.com)