Way of operating that's not quite ideal (4)
I believe the answer is:
mode
'way of operating' is the definition.
(I've seen this before)
'not quite ideal' is the wordplay.
'not quite' means to remove the last letter.
'ideal' becomes 'model' (model is a kind of ideal).
'model' with its last letter taken off is 'MODE'.
'that's' is the link.
(Other definitions for mode that I've seen before include "Way, style" , "Way of operating" , "Trend" , "Fashion; way of performing" , "Style, method" .)