In total area length and line related (3,4)
I believe the answer is:
all told
'in total' is the definition.
(I've seen this before)
'area length and line related' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'length' becomes 'l' (abbreviation in geometry).
'and' means one lot of letters go next to another.
'line' becomes 'l' (used when specifying particular lines from a poem).
'related' becomes 'told' (I've seen this before).
'a'+'l'+'l'+'told'='ALL TOLD'
(Other definitions for all told that I've seen before include "book reading's finished?" , "To summarise" , "Altogether" , "In total" , "In summary" .)