A web hosting service is a type of Internet hosting service that allows individuals and organizations to make their website accessible via the World Wide Web.
Web hosts are companies that provide space on a server owned or leased for use by clients, as well as providing Internet connectivity, typically in a data center.
Web hosts can also provide data center space and connectivity
to the Internet for other servers located in their data center.
The availability of a website is measured by the percentage of a year in which the website is publicly accessible and reachable via the Internet. This is different from measuring the uptime of a system. Uptime refers to the system itself being online.
Uptime does not take into account being able to reach it as in the event of a network outage. A hosting provider’s Service Level Agreement may include a certain amount of scheduled downtime per year in order to perform maintenance on the systems. This scheduled downtime is often excluded from the SLA timeframe, and needs to be subtracted from the Total Time when availability is calculated. Depending on the wording of an SLA, if the availability of a system drops below that in the signed SLA, a hosting provider often will provide a partial refund for time lost.