Instant tea or coffee (5)
I believe the answer is:
mocha
'coffee' is the definition.
(type of coffee drink)
'instant tea' is the wordplay.
'instant' becomes 'mo'.
'tea' becomes 'cha' (cha is a type of tea).
'mo'+'cha'='MOCHA'
'or' acts as a link.
(Other definitions for mocha that I've seen before include "Dark brown" , "Kind of coffee" , "Yemeni port; type of coffee bean" , "Strong dark coffee" , "Deep brown; a fine coffee" .)