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1.
An ass that is so flat and unremarkable that it appears as though a person's legs are hooked directly to their back, and there is no ass in between. People with ass leg syndrome frequently wear pants that jack way up their crack, usually causing shit stains in their undergarments. People who are afflicted with this particular abnormality do not ever get laid because candidates for sexual activity have significant difficulty in finding the ass legged person's crotch, which is of course a prerequisite for sex.
Dude1: Damn, I'm really drunk and I need to get laid. I'd fuck that chick over there, but she's got an ass leg.

Dude2: Yeah, well you're mom's got an ass leg too, but that didn't stop your dad. How did he ever find youre mom's pussy anyway? Her ass leg would've thrown me off while hunting for her snatch.
by EatMyJunk April 27, 2009
 
2.
Legs (thighs) that are so big it makes the persons butt look smaller in comparison.
Person: Wow that girl has no butt
Person2: nah she just has Ass Legs
by C-C-C-CherryBomb October 04, 2010
 
3.
When so much of the top of the girl's leg is exposed that it shows the bottom curve of the ass.
That girl's booty shorts are showing assleg.

The wind blew so hard that the skirt showed assleg.
by Big Lumberjack February 24, 2009