Domain names are used to identify one or more IP addresses. For example, the domain name, microsoft.com, represents about a dozen IP addresses. Domain names are used in URLs to identify particular webpages. For example, in the URL https://www.password-sentry.com/, the domain name is password-sentry.com.
Every domain name has a suffix that indicates which top level domain (TLD) it belongs to. There are only a limited number of such domains. For example:
gov - Government agencies
edu - Educational institutions
org - Organizations (nonprofit)
mil - Military
com - commercial business
net - Network organizations
ca - Canada
In the case of password-sentry.com, the TLD is com.
Because the Internet is based on IP addresses, not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses.