The gTLD are the generic Top Level Domains. The “old” Top Level Domains are .com, .org, .net etc..
Another historic player in the domain names field is the ccTLD ( .ch, .de, .us etc.. ), which have a different organization and setup.
There are, since a bit more that one year, new gTLD. Some are meaningfull – .ski, .guru, .kitchen, some are very generic – .xyz, and some are representing brands – .bmw, .axa for instance.
These new domain names are enjoying a rapidly growing popularity, even though it is not really known to the public. Google’s new “mother company”, alphabet’s website is “abc.xyz”. That is a new gTLD website.
There are so far around 730 new Top level domain names. The number of domains on new gTLD has reached 7 million just before mid august. The growth of domain numbers is much higher than domains created on “old” gTLD, who grew in the same period of approx 4 million domains. The total domains on old gTLD is today 152 million, so the gap is still huge.