Real World article
(written from a Production point of view)

Referenced in the final draft script of the Star Trek: The Original Series episode "Miri", "mommies" was a slang term used by Onlies, meaning "can openers".

The term was used in a discussion between Miri and James T. Kirk. Miri revealed to Kirk that the Onlies had "lots of mommies and cans," if they're hungry. As Kirk was puzzled by the word "mommies", Miri explained it meant "can opener things" and went on to comment, "Can opener is a dumb word. We found kind of a fresh word, maybe...."