____ was the main activity in the TV show Whose Line Is It Anyway (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
improv
(Other definitions for improv that I've seen before include "Stand-up comedy, perhaps" , "Off-the-cuff comedy" , "little ad-libbing" , "off-the-cuff humour" .)