Flowing in the bar (6)
I believe the answer is:
legato
'flowing' is the definition.
(musical term)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for legato that I've seen before include "Smoothly (mus.)" , "Smoothly-flowing" , "scored smoothly" , "Smoothly (musical)" , "In a smooth and flowing manner (music)" .)