What should I refer a code to?

Questions
1

so, I know you would refer to the username/email as < U S E R > and the password as < P A S S > but lets say I want to do like a singe code of numbers, what would I put for that?

2 
[WORDLIST TYPE]
Name=Numeric
Regex=^[0-9]*$
Verify=False
Separator=:
Slices=CODE
3

thank you! This helped me alot!