Each registered domain name has a minimum of two Name Server records that show where it's hosted i.e. by using these records you point your domain name to the servers of a specific hosting provider. That way, you have both your site and your emails handled by the very same company. On the lower level of the Domain Name System (DNS), nevertheless, there are a number of other records, for example A and MX. The former shows which server deals with the site for a given domain and is always an IP address (188.8.131.52), while the second one shows which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). As an illustration, whenever you enter a domain in your browser, your request is directed through the global DNS system to the provider whose NS records the domain name uses and from there you will be forwarded to the servers of another company provided you have set an IP address of the latter as an A record for your Internet domain. Having different records for the site and the emails means that you may have your site and your emails with two different providers if you would like.