- A repeated instrumental melody line in a song.
- A clever or witty remark.
- A variation on something.
- A spoof.
What the trio are doing are basing short one or two page stories based on my Black Tower strips or characters so a "riff" in that case can be 2-4 above. In the old days we might have put "after Terry Hooper" but that is quite long so a "riff" says all that.
I know some non-English speaking visitors may find our terminology odd -you can always ask if something confuses you!
There. Riff explained.