It describes letters to pals perhaps (6)
I believe the answer is:
postal
'it describes letters' is the definition.
The definition suggests a singular noun but the answer is not.
'to pals perhaps' is the wordplay.
'perhaps' indicates an anagram.
'to'+'pals'='topals'
'topals' is an anagram of 'POSTAL'.
Can you help me to learn more?
(Other definitions for postal that I've seen before include "Relating to mail service" , "Type of order" , "to go so mad in America" , "Relating to mail delivery" , "To do with snail mail" .)