What will happen If i limit Restful api

I am taking a guess on these because what I  have found is that there are different
fields for the different types of auth systems out there.

user_id        - The users ID
key            - The users private secret key
level          - The users logon level
ignore_limits  - Weather to ignore limits or not
is_private_key - Is this secret key private
ip_addresses   - list of client ip addresses
date_created   - The date the user was created

Do you know what is level list? and what is ignore_limits