A stage of Web development at which the site is finished and launched. For example, you may hear, "When is the site going to go live?" It means the same as "up," in the sense that someone could respond by saying, "It'll be up by the end of the business day on Friday." Most Web developers will wait until the middle of the night to FTP a finished site to the server (unless they've tested it thoroughly on a staging server). There is less traffic on the Net at odd hours of the night, so they can presumably get it up quicker and fix anything that may be wrong (or "broken") without the majority of their audience witnessing the error.
NetLingo Classification: Online Jargon