It describes a lot - somehow her mum heard ten (5,3,6)
I believe the answer is:
under the hammer
'it describes a lot' is the definition.
(a lot in an auction goes under the hammer)
'somehow her mum heard ten' is the wordplay.
'somehow' indicates an anagram.
'her'+'mum'+'heard'+'ten'='hermumheardten'
'hermumheardten' anagrammed gives 'UNDER THE HAMMER'.
(Other definitions for under the hammer that I've seen before include "a lot?" , "Lots come here" , "Ensure your thumb is not" , "For sale by auction" , "on the block" .)