From my point of view , a riff is a repetitive series of notes used as part of the main rhythm section ( sometimes but not always , replacing a chord progression ) , I am not sure , but it probably started with the blues and spread from there . Listen to " Damn right I've got the blues " by Buddy Guy , play a chord progression over it and it sounds crap , there is something missing , Other examples are Led Zeppelin , Black Sabbath , Cream and a lot of metal bands are all riff based . A lick is part of a solo , played over a riff or chord progression . Licks are a couple of bars long that are broken down from a solo . It would be almost impossible to learn a solo note for note from beginning to end , but if you break it into sections that are played in different positions on the fretboard , it becomes manageable . Licks are also used to enhance the melody ( call and response ) or emphasise chord changes ( a turnaround is a lick ) Hope this helps