A domain registrar plays a crucial role in internet services by managing the registration of domain names. These organizations are accredited by the Internet Corporation for Assigned Names and Numbers (ICANN) or national authorities, ensuring that domain names are unique and properly assigned. When individuals or businesses register a domain through a registrar, they gain ownership of that specific web address for a set period. Registrars also offer additional services like DNS management and email hosting, contributing to a comprehensive online presence.