A domain in "Registrar Lock" status means the registrar for that domain has locked the domain to prevent any unauthorized domain transfers as well as any changes made to that domain's settings. Usually, the actual registrant has a setting in their account that allows them to lock or unlock their domain at will (this is the case with Dynadot accounts).

A domain can also be in registrar lock mode if the domain has already expired. At this point, usually the domain cannot be transferred to another domain registrar, and you will need to renew the domain with the current domain registrar.