Like a remix, but remixing the lyrics of a song off the top of your head, to match that of an already existing song. Usually trying to keep the same tempo, and rhyme scheme of the original song, but not always.
Example of a FreeMix:
Grenade by Bruno Mars, after a quick FreeMix in the car, quickly turns into a song about your bro jumping on the Grenade for you, so you can bang out the hot friend:
♫I'd jump on the grenade for ya!♫
♫Fuck a bitch with AIDS for ya!♫
♫Bust a nut on her face for ya!♫
Grenade by Bruno Mars, after a quick FreeMix in the car, quickly turns into a song about your bro jumping on the Grenade for you, so you can bang out the hot friend:
♫I'd jump on the grenade for ya!♫
♫Fuck a bitch with AIDS for ya!♫
♫Bust a nut on her face for ya!♫
by Jacob Sportsman January 2, 2011