downtime

 downtime  is the time period or duration while a site, whether indieweb, commons, or silo, is offline and unreachable.

IndieWebCamp 2015-05-29
For a period of hours, due to lengthy problems including power outage at the hosting provider, IndieWebCamp.com and various related services like IndieAuth.com were down and unreachable.

Silo Examples
Lots. See Individual silo pages and add links here.
 * Facebook
 * G_Suite
 * GitHub
 * Tumblr
 * Instagram
 * Twitter

Hosting Examples

 * AWS
 * CloudFlare
 * Dreamhost
 * iCloud

Other Examples

 * Internet_Archive
 * W3C