Here you are: https://docs.mql4.com/basis/preprosessor/constant
It's a constant . .
AddP() might be a funtion that someone has created themselves . . . read about it here: https://docs.mql4.com/basis/functions
int AddP (double a, double d=0.0001, int n=5, bool b=true, string s="passed string")
Print("Required parameter a=",a);
Print("The following parameters are transmitted: d=",d," n=",n," b=",b," s=",s);