Uptime in context of Web Hosting Service, is the web server working time without failures. Uptime is important measure, because it indicates web hosting servers and maintenance quality. Uptime is the amount of time that a server has stayed up and running. This is usually listed as a percentage, like "99.9% uptime." Uptime is a great measure of how good a web hosting provider is at keeping their systems up and running. The most basic thing for a website to be found on the internet depends on whether the server where the files are stored is online i.e. up and running at any given time. This is called Server Uptime. You will find that most of the web hosting providers will claim a 99.99% server uptime. Some even claimed 100%. If you have time, search for comments by users of the provider on internet forums or elsewhere online. Or go for the larger more established hosting companies who have built a trusted reputation. Most good hosting companies have multiple server data and power backups. A few also promised 100% and they do that by guaranteeing refund of fees in the eventuality that any downtime might happen.