Uptime

Uptime refers to the amount of time a service or web site has been operational and functional. It typically is used to refer to the reliability of a service; and hitting greater than 99.99 percent or higher uptime is required for online services which serve high volume websites.

An uptime percentage of 99.99% in a single year refers to 0.01% downtime in a 365 day year which is the equivalent of:

365 x 24 x 60 x 60 x 0.0001 = 3154 seconds down = 52 minutes per year