Hi Marion! IMHO...

In my little world, a "riff" usually refers to a instrumental phrase that repeats throughout a song, often the catchy rythm part. Sometimes it could be the "hook" i.e. (a R&R tune comes to mind) the guitar "riff" at the beginning and throughout Roy Orbison's Pretty Woman. C.C.R. made a career of Riff Rock as does John Fogerty to this day. The main riff usually makes a song instantly identifiable to the listener. Often, it's the first and only part learned, which can be frustrating at jams.

I've always thought of a "lick" as a short series of notes played as a solo would be played. The lick might be inserted between vocal lines (i.e. The Sultans of Swing by Dire Straits), or between verses and so on. It might even repeat as a riff could, but not as commonly. A good guitar solo is a series of licks that flow nicely one into the other, with nice phrasing to give it feel.

Just another opinion... Thanx