A top-level domain is the last part of the domain name after the "dot". It is also know as domain suffix. There are two different categories of top level domains - country-specific top-level domains, and generic top-level domains.
With top-level domains you can identify certain website elements, such as, the business type, the country of origin,type of website - if it’s a government site, school website, and more.
.COM is the most popular TLD and therefore, is used by many brands.