Slidings played across the middle of piano (9)
I believe the answer is:
glissandi
'slidings played across the middle of piano' is the definition.
I can't tell whether this definition defines the answer.
'slidings played across the middle of piano' is the wordplay.
'played' indicates an anagram (letters playing around).
'across' is an insertion indicator.
'the middle of' says to take the centre.
The middle of 'piano' is 'a'.
'slidings' anagrammed gives 'glissndi'.
'glissndi' going around 'a' is 'GLISSANDI'.
Can you help me to learn more?
(Other definitions for glissandi that I've seen before include "Players may perform them" , "playing, while sliding up and down the passages" , "Series of rapidly ascending or descending musical notes" , "showing smooth actions" , "Musical terms" .)