Absolute value is recurrent problem, with board game involved (7)
I believe the answer is:
modulus
'absolute value' is the definition.
(modulus is a kind of absolute value)
'recurrent problem with board game involved' is the wordplay.
'recurrent' is a reversal indicator (recurrent can mean turning back).
'problem with' becomes 'sum' (I am not sure about this - if you are sure you should believe this answer much more).
'board game' becomes 'ludo' (ludo is a kind of board game).
'involved' indicates putting letters inside.
'sum' placed around 'ludo' is 'suludom'.
'suludom' reversed gives 'MODULUS'.
'is' is the link.
(Other definitions for modulus that I've seen before include "Harold -, former PM" , "Absolute value" , "A number's magnitude regardless of sign" , "Magnitude of a number without regard to sign" .)