domains
There are authorities that have the task of managing the domain system.
Sites like GoDaddy are middleman between the authority and clients, and offer extra features on top of just registering the domain.
top level domains (tld) and second level domains (sld)
example: test.hi.com
.com is tld
test.hi is sld
dominican domains .do
the Authority is NIC. https://www.nic.do/. on their site they sell domains directly for the cheapest price.
for this domain, looks like the authority has the ability to manage some second level domains separate from the top level domain.
list of second-level these domains here: https://en.wikipedia.org/wiki/.do
2k DOP for .do and 800 DOP for second level domains
this allows someone to register x.do and someone else to register x.com.do
some middleman sites I found are: