Every single registered domain has no less than 2 Name Server records that show where it is hosted i.e. by using these records you direct your domain to the servers of a specific website hosting company. In this way, you've got both your website and your emails managed by the same provider. On the lower level of the Domain Name System (DNS), on the other hand, there are lots of other records, for example A and MX. The former reveals which server manages the site for a given domain name and is always an IP address (22.214.171.124), while the second one shows which server handles the emails and is always an alphanumeric string (mx1.domain.com). For example, whenever you type a domain address in your browser, your request is forwarded through the global DNS system to the provider whose NS records the domain name uses and from there you may be forwarded 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 independent records for the site and the e-mails means that you could have your site and your emails with two different companies if you wish.