What is the purpose of the third and fourth DNS records?

When modifying DNS records, domain registrars offer four areas for customization, while hosting providers only require two. What functions do the remaining two areas serve?

In order to successfully register a domain name, two separate DNS servers (two records) with different IP addresses are required, according to registration regulations. To complete registration, the hosting provider must transfer the domain name along with at least two DNS records to the registrar.

The purpose of requiring two records is to increase reliability; if the first DNS server is inaccessible, the second one can be used as a backup. Sometimes, registrars allow for registering two records with the same IP addresses. While this does not impact the domain's operation, it may result in the domain being inaccessible in the event of a potential failure or unavailability of those IP addresses.

Additional entries beyond the first two DNS records are available to add more DNS servers, necessary for ensuring domain operation even in the event of a failure of the initial two servers. Adding a third and fourth DNS server can increase stability and help maintain domain access.