This will add hostmasks to your Operator definition. Hostmasks are used to prevent people from gaining operator status on your server from systems that you haven't defined. It is very important that you add proper masks to each operator definition.
ADD - Add a mask to an operator definition.
DEL - Remove a mask from an operator definition.
LIST - List all of the masks attached to an operator definition
/as help oper access <topic>
An operator will only be able to gain access to operator privileges when matching one of the masks in the operator definition. It is important that all addresses that may be used are included in the operator definition. Requiring matching addresses is an additional level of security, although the password for the operator access should be the primary method of security. Always make sure that operators have secure passwords.