A Top Level Domain is the .com in example.com.   There are many Top Level Domains for various purposes.   The most common of them is .com, but there hundreds of others.   The importance of having a .com TLD is not as significant as it was in the early 2000s.   Many sites are using less formal domain names to suit their purpose.  The concern was representation or other companies registering the .com domain for companies that had decided to go with another TLD.

Say for example, an example company registered example.net.   A rival company then registers example.com, and points that web traffic to their business.  An individual looking for example.net might be persuaded to go to example.com because it has more name recognition.