A website (domain) hosting company has computers that hold web sites and serve these
websites to the public. These computers are called 'servers' because they serve
web pages to the public.
There are literally thousands of domain hosting companies across the world and there are
just as many features available from these companies.
The server is responsible for making your website available to the public 24 hours per day.
They(we) do this by updating their computers often and running backup software just in case
something does happen and the server loses any data. There is always a backup available that
can be online within minutes.
The server almost always has a backup power source available just in case the power to their
computers shuts down. Usually backup diesel generators will start automatically after power is
down for a short period of time.
The domain hosting company is responsible for all these computers and data and they also have
to pay for backbone providers across the nation.
Hosting companies provide computers (servers)
that are especially configured for this type of application.