Percentage of quota falling short (5)
I believe the answer is:
ratio
'percentage' is the definition.
(I've seen this before)
'quota falling short' is the wordplay.
'quota' becomes 'ration' (I've seen this before).
'falling short' means to remove the last letter.
'ration' with its last letter removed is 'RATIO'.
'of' acts as a link.
(Other definitions for ratio that I've seen before include "Proportional relationship" , "Comparative figure" , "Relationship of numbers" , "eg 1:3" , "Quotient of two numbers" .)