Uptime is the measure of the uninterrupted time that a hosting system experiences. Ideally uptime would be at 100% (i.e. zero downtime) but in the real world this is extremely difficult to achieve. In layman’s terms, Uptime is the number of hours that a server is working and available and is the opposite of downtime.
Uptime is important because it means that your hosting is available. If your site is not available then obviously this has a negative impact on your business. Customers and potential customers can not see your website so you may lose business. You can not send or receive emails. Search engines may see that your website is unreliable which negatively impacts your ranking.
Uptime is calculated based on the number of hours that the system (server) is available during a given period of time and is expressed as a percentage.
Clients can rest easy knowing their website will rarely experience downtime, if ever. This guarantee is made over the course of a year. A 99.9% uptime means your site won’t experience more than 8 total hours of downtime due to server issues throughout the year (there are 8,765 hours in a year).