look up any word, like ethered:
 
1.
Unflattering description of an older woman's big, fat, lumpy, out-of-shape, cellulite butt.
Dude, your new ho has a big, fat mom butt.
by JohnstonGuy July 28, 2005
 
2.
To have a butt as large as an older female.
That guy Beau has Mom Butt.
by V. Long August 12, 2003
 
3.
When a female (usually an older woman, particularly a mother) wears unflattering, waist high jeans that give the buttocks a flat, unappealing look. It may sometimes entail wearing sweat pants bought from your local Walmart. Also note the buttocks may possibly look as if there is a large amount of cellulite. Either way, you don't want that.
Those Dungarees totally give that girl a mom butt, but I am desperate..
by TrustMe, Really November 12, 2009
 
4.
Mombutt happens almost immediately after the birth of a ladies first child. The hips widen from birth, stretching the cheeks to appear much flatter. There will be a slight upside-down heart shape starting a the center crack. That outlining will sink back down into the thigh with the finish of every step. Mombutt may deviate, but will always start with the presence of Mompants.
by World's Greatest Mom July 06, 2009