Period recalled in spectacular exhibition (3)
I believe the answer is:
era
'period' is the definition.
(era is a kind of period)
'recalled in spectacular exhibition' is the wordplay.
'recalled' says the letters should be written in reverse.
'in' indicates the answer is hidden within the clue.
'are' is hidden in the letters of 'spectacular exhibition'.
'are' written backwards gives 'ERA'.
(Other definitions for era that I've seen before include "Important time" , "Age of importance" , "Period, age" , "Stage" , "generation, maybe" .)