Spot bishop's promotional copy (5)
I believe the answer is:
blurb
'promotional copy' is the definition.
(copy or text promoting a book)
'spot bishop's' is the wordplay.
'spot' becomes 'blur' (blur can mean a blurry spot).
'bishop' becomes 'B' (chess abbreviation).
'blur'+'b'='BLURB'
(Other definitions for blurb that I've seen before include "Promotional guff" , "Publisher's write-up" , "Short description on book cover" , "Promotional text for a book" , "stuff on jacket" .)