Hi,
You should take a glance on this SDK Chapter: Reverse Polish Notation.
In Reverse Polish Notation (RPN), sp0, sp1, etc are registers where informations can be stored.
In your case, the value 1 is stored in the first register sp0 and the variable L:A320NX_EFIS_L_OPTION is interpreted like a enum (-1, 0, 1, etc) then compared to the value 10 in order to be identical. If yes, the calculation continue.