Rubbish blurb about energy (6)
I believe the answer is:
rubble
'rubbish' is the definition.
(rubble is a kind of rubbish)
'blurb about energy' is the wordplay.
'about' is an anagram indicator.
'energy' becomes 'e' (physics symbol as in E=mc2**).
'blurb' with letters rearranged gives 'rubbl'.
'rubbl'+'e'='RUBBLE'
(Other definitions for rubble that I've seen before include "Demolition site debris" , "Debris, detritus" , "Debris left after building or demolition" , "Waste fragments of stone or rock, debris" , "Bits of demolished building" .)