I fail to recall this word (could be informal in nature) that refers to the 'warmth of a seat that has just been vacated by someone seated on it for some time'.
Let me go ahead and coin "posterior thermoresidual."
Urbandictionary has the following slang terms:
The residual warmth left over on a toilet seat after a man or woman has taken a crap, and or mearly sat there undressed for a period of time. The life force that sustains warm seat warriors.
When I sat down on the bowl I was pleasently surprised (disgustingley horrified) by the residual man heat left by my roommate.
The uncomfortable warm feeling you get after sitting in a seat that was previously occupied by a "fluffy" person with a huge butt.
"Ewww, that lard butt left post-rectal warmth in my seat!"
The residual warmth on a chair or toilet seat from someone else's butt.
I sat down on the throne in stall 2 and I knew that Carl had just been there from all the ass heat.
Image source: http://imgur.com/gallery/foIrRK7
Thermal buttprint, akin to thermal handprint.
Where I'm from we call it Firepad, although that typically assumes the person who was formerly sitting in the chair farted as well.