Actual are actual, notional is the money won less any class sponsorship, etc that goes on your card for class limits.
I'm sure someone will explain it better
Actual is the money you take home, Notional is the money you get graded on which is LESS than the actual so you can stay jumping in the lower classes longer.
Different venues have different prize money so to make records all equal they have notional/actual. Actual is the actual prize money you get. Notional is the money thats recorded on your card