Patches are cumulative, version-specific updates, built to resolve a customer-specific issue on a production deployment.  In general terms, patches should only be applied to customer environments that are experiencing specific behaviors addressed by a given patch version.  Patches are available for all customers with an active support agreement and may be requested by completing the Request Form linked here.  Square 9's fulfillment team will always deliver the most current patch version.  Again, all patches are cumulative.