Busy gathering of people requiring couple to swap places (7)
I believe the answer is:
teeming
'busy' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for teeming that I've seen before include "Swarming in to meeting" , "Abundant" , "Full of, abounding in" , "Alive" , "Chock-a-block" .)