Bottleneck improvisation on record (6)
I believe the answer is:
Here is my best explanation:
'bottleneck' is the definition.
(I've seen this before)
'improvisation on record' is the wordplay.
'improvisation' becomes 'jam'.
'on' says to put letters next to each other.
'record' becomes 'log' (logging is a kind of recording).
'jam' after 'log' is 'LOGJAM'.