Every registered domain name has no less than 2 Name Server records which show where it is hosted i.e. by using these records you point your domain name to the servers of a specific website hosting company. That way, you have both your website and your e-mails managed by the same company. On the lower level of the Domain Name System (DNS), however, there is a variety of other records, such as A and MX. The former shows which server deals with the website for a given domain address and is always an IP address (123.123.123.123), while the second one reveals which server deals with the emails and is always an alphanumeric string (mx1.domain.com). As an example, any time you enter a domain in your browser, your request is sent through the global DNS system to the company whose NS records the domain uses and from there you may be forwarded to the servers of a different service provider provided you have set an IP address of the latter as an A record for your domain address. Having separate records for the website and the e-mails suggests that you may have your site and your emails with 2 different providers if you would like.