Starting with Drupal 8.0.0, Drupal core releases will move to a new release cycle schedule, and begin using the semantic versioning (semver) numbering system. (For a video overview of semver you can watch this Semantic Versioning video.)
Drupal 6 support will be dropped three months after 8.0.0 is released.
Patch releases (8.0.1, 8.0.2 etc.) will have a monthly release window, which will address bugs to be fixed.