The main purpose of a domain registrar in internet services is to manage the reservation of internet domain names. Domain registrars facilitate the purchase and renewal of domain names, ensuring they are unique and available for use. They also provide relevant services, such as DNS management and domain privacy protection. By acting as intermediaries between domain name registries and users, registrars ensure that individuals and organizations can establish their online presence securely. Additionally, they play a role in compliance with policies set by governing bodies like ICANN.