look up any word, like ratchet:
 
3.
A phrase used for a uncommon sexual manuever. "Fire Down Below" is accomplished only by setting a females pubic area on fire, and then extinguishing the flames with your own semen.
"Yeah, she wanted to get kinky, so I pulled out the Zippo, lit her shit on fire, then put it out with my cum. Perfect execution man."
by John Boy December 23, 2003
 
1.
A descriptive meaning horny, hot and bothered, ready to go (sex). The term comes from the warmth given off by female (and male) genitailia when they are in a heightened state of sexual arousal.
"How was your date?"

"Awesome, dude! She had the fire down below, so we didn't stay long at the bar!"
by -E1 July 16, 2008
 
2.
A term for cystitis, an inflammation of the bladder causing a buring sensation and painful urination. May be caused by vigorous and/or frequent sex. Or not knowing how to wipe your arse properly.
"Why are you looking so unhappy?"
"I have fire down below."
by Silverfin September 17, 2006