The exact opposite, or even extreme opposite of a Milf (Mother I'd Like to Fuck). A Minef stands for A Mother I'd Never Ever in my nastiest dreams Fuck. This noun can be used to describe women of grotesque figures and or appearances in general.
Scenario 1- MILF
Dave: Man, Jesse, don't you think Jina's mom is such a MILF? I'd tap that.
Jesse: Dude I totally agree. I heard she used to be a playboy model, thats why mannn.
Scenario 2- MINEF
Dave: Man, look at Jina's mom. Is it me or did she gain 50 pounds over the summer?
Jesse: That's sick man. Her rolls jiggle. She's a total MINEF. No doubt bout that.