Outlook: s+/s plus origins

S+ is shorthand for "Schedule +". It no longer exists but it remains in the vocabulary. It is the same as a meeting request.

S+ or Sched+: I don't think we'll ever banish this from the lingo. Schedule+ hasn't existed as a product for many years, and yet most softies (even people who joined the company long after S+ stopped existing) refer to scheduling meetings as Sched-plus. The typical usage is something like this: “Ess Plus me on that.“ In 98 or 99, a few testers on Outlook tried valiantly to get the company to use the phrase “outcal“, but it never caught on.

Read more at http://blogs.technet.com/b/kclemson/archive/2004/05/05/126940.aspx and http://scobleizer.com/2006/08/18/richard-tells-me-to-explain-my-view-on-google-calendar/