Every registered domain has no less than 2 Name Server records that show where it is hosted i.e. by using these records you point your Internet domain to the servers of a particular hosting company. In this 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), however, there are a number of other records, like A and MX. The former shows which server handles the website for a given Internet domain and is always an IP address (188.8.131.52), while the second one indicates which server handles the emails and is always an alphanumeric string (mx1.domain.com). For instance, whenever you type a domain in your web browser, your request is forwarded through the global DNS system to the provider whose NS records the domain uses and from there you may be forwarded to the servers of a different provider in case you have set an IP address of the latter as an A record for your Internet domain. Having different records for the website and the e-mails means that you could have your website and your e-mails with two different providers if you'd like.