Unwelcome messages about charts (4)
I believe the answer is:
spam
'unwelcome messages' is the definition.
'spam' can be an answer for 'messages' (I have seen 'unsolicited messages' mean 'spam' so perhaps 'messages' could also mean 'spam'). I am not sure about the 'unwelcome' bit.
'about charts' is the wordplay.
'about' says the letters should be written in reverse.
'charts' becomes 'maps' ('map' can be a synonym of 'chart').
'maps' written backwards gives 'SPAM'.
Can you help me to learn more?
(Other definitions for spam that I've seen before include "Tinned meat - unwanted email" , "one doesn't want on computer" , "Unwelcome approach" , "Food" , "Tinned processed meat" .)