Five years after its release, the largely forgotten Windows Vista is moving out of the "mainstream" support period. Starting today, consumers will still get security updates for free, but everyone without a commercial support contract will need to pay for bug fixes or other patches. In April 2017, this "extended" support will also end, and both consumer and commercial users will be on their own, without security or other updates (although security fixes may be offered in special cases.)
That final cutoff date is approaching rather sooner for Windows XP users, who now have two years to upgrade to a new OS before extended support cuts off. XP stayed in mainstream support for several years longer than Vista, which got only the minimum five years. That's only indirectly because of XP's popularity, though: Microsoft tailors its support period based on how long it's been since the latest version of Windows was released, and there was a significant gap between XP and Vista. Microsoft has more information on its lifecycle page.