A Freestyle Rap can be made up of Lyrics that U wrote but yet, they are not to be fitted for any song you're doing. you jus have alot of hot Rhymes in there of sum shit u jus wanted to say and however U really wanted to say it..
and then u have Freestyle Rapping or just regular Freestyling where u jus go in an do this shit off the top of your head.
Common, KRS-ONE, Eyedea, Mos Def, MC Juice, Supernatural, and Sage Francis all Freestyle off the top of their heads..
While Murda Mook, T-Rex, Loaded Lux, Math Hoffa, Goodz, Arsenol, Reed Dollaz, and Cysserro, they all Write their shit down, but its not really fit for a song. they just random hot punchlines they can use in battles or whatever. so they good at making Freestyle Raps on sum random shit.