a middleman is a person that holds funds/secures the item in a deal of 2 persons
"How much for this 3letter insta"
"$250 btc"
"That sounds sketchy, can we use a mm?"
"Yes, u pay the mm fees"
*Seller gives the item to the mm*
*Mm confirms that he has the item and secures it, tells the buyer to send the btc*
*Btc is received*
*Buyer gets the item*
Deal is done
For more than one individual to masturbate whilst in the company of another/others doing the same. MM is an abbreviation of the words mutual masturbation.
In terms of a lover, future Mother of your children. Often used to subtly declare ones affection for ones relationship with a caring soul. Transcending the stigma of society, without prying eyes being aware of your dedication.