Every domain name which is registered and hosted has a lot of DNS records - some of them are set up automatically when you host a domain, others can be created by hand if necessary. As an illustration, the A record of a domain name is its IP address i.e. this record reveals where the website is located; the MX records show where the emails are stored, while with an SRV record you can use a domain address for unconventional purposes, such as a Voice-over-IP service. The ability to set up and modify specific records permits you to have different services with different companies if, for illustration, your current host provides good web hosting, but has troubles with the email service, or you simply prefer to get a certain service from a certain company. Even though you can create and edit these records freely and with no limits as you own a given domain name, a lot of companies charge extra to give you this option.