gTLDs, or generic top-level domains, are general purpose domains and are some of the most common TLDs on the web although there are a limited number of such domains.
They generally have three or more characters and can be subdivided into two types:
‘Sponsored’ TLDs (sTLDs)  - these can be registered by anyone. 
‘Unsponsored’ TLDs (uTLDs) – these can only be registered by certain groups of people who meet the eligibility requirements.

In the 1980s, ICANN (The Internet Corporation for Assigned Names and Numbers) created seven gTLDs - .com, .net, .org, .int, .edu, .gov, and .mil. Three of these .com, .net, and .org are sponsored and may be registered without restriction; the other four have limited purposes.