In
music a riff is a repeated instrumental
melody in a song like that catchy guitar
lick from Black Sabbath's "Iron
Man." It also means to improvise in your performance, esp. by expanding on something recognizable. So another artist might start with Sabbath's "Iron
Man"
melody at a live show and then take it in completely different direction.
"
Man that's a sick guitar riff in that Metallica song Enter Sandman"
"I saw this great improv jazz band that could really riff."
The term is also often used to describe inspiration and improvisation in other things like acting, comedy, dancing, drawing, djing/scratching etc.
a b-boy might say, "So, I was breakin with Jamil the other day and was feelin what he was doin so I started riffin off his style and adding some new flava to it. I vibed off his uprock but threw in some popping and dropped down to a wind mill...It was dope."
an mc might say, "Yo me and my boy were in a cipher last
night and we just started to riff off each other, we were just lettin it
flow back and forth, ya
know what I'm sayin."