Food fad is ultra silly (5,5)
I believe the answer is:
fruit salad
'food' is the definition.
(fruit salad is a kind of food)
'fad is ultra silly' is the wordplay.
'silly' indicates an anagram.
'fad'+'is'+'ultra'='fadisultra'
'fadisultra' is an anagram of 'FRUIT SALAD'.
(Other definitions for fruit salad that I've seen before include "Oranges and Lemons etc" , "Dessert served in syrup or juice" , "Possibly healthy dessert" .)