Symbolic maths (7)
I believe the answer is:
algebra
'symbolic maths' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for algebra that I've seen before include "Symbol-based mathematical calculation" , "'Branch of mathematics, uses letters and symbols (7)'" , "Maths with letters representing numbers" , "Branch of mathematics using letters and symbols" , "Numbers and letters branch of maths" .)