Each registered domain has a minimum of 2 Name Server records which show where it's hosted i.e. by using these records you point your Internet domain to the servers of a particular website hosting provider. That way, you have both your website and your emails managed by the same service provider. On the lower level of the Domain Name System (DNS), on the other hand, there is a variety of other records, for instance A and MX. The former shows which server manages the website for a given Internet domain and is always an IP address (18.104.22.168), while the second one shows which server deals with the emails and is always an alphanumeric string (mx1.domain.com). For instance, any time you type a domain address in your browser, your request is forwarded through the global DNS system to the company whose NS records the domain name uses and from there you will be directed to the servers of another service provider in case you have set an IP address of the latter as an A record for your domain address. Having different records for the site and the emails suggests that you may have your site and your emails with 2 different companies if you'd like.