Generic Top Level Domain (gTLD) do not belong to any countries, and include the original four .COM, .NET, .ORG, and .BIZ extensions.
Starting in 2012, the gTLD market expanded to also consist of New Generic Top Level Domains (ngTLD) such as .APP, .BANK, .FUN, .INSURANCE. With new gTLD's being released there is sure to be a TLD for everyone. There are over 600 new gTLD's currently available at 101domain.com.
gTLD's typically have no restrictions. There are exceptions to the rule such as .BANK, .INSURANCE, .JOBS, .APP etc. These extensions have restrictions and/or requirements as described on the website.
Today the number of gTLD extensions exceeds 1,200.