Each registered domain has no less than two Name Server records that show where it's hosted i.e. by using these records you direct your domain to the servers of a particular hosting company. In this way, you have got both your site and your e-mails managed by the very same provider. On the lower level of the Domain Name System (DNS), on the other hand, there are lots of other records, like A and MX. The first one reveals which server handles the site for a given domain address and is always an IP address (188.8.131.52), while the latter shows which server manages the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, when you type a domain name in your web browser, your request is sent through the global DNS system to the provider whose NS records the domain 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 name. Having independent records for the website and the e-mails suggests that you could have your website and your emails with 2 different providers if you'd like.