The Apex Flex Queue pilot enables you to submit batch jobs beyond the allowed limit of five queued or active jobs. Any jobs that are submitted for execution but aren’t processed immediately by the system are in holding status and are placed in a separate queue (the Apex flex queue). Up to 100 batch jobs can be in the holding status. When system resources become available, the system picks up jobs from the Apex flex queue and moves them to the batch job queue. The status of these moved jobs changes from Holding to Queued. Queued jobs get executed when the system is ready to process new jobs.
Without administrator intervention, jobs are processed first-in first-out—in the order in which they’re submitted. Administrators can modify the order of jobs that are held in the Apex flex queue to control when they get processed by the system. For example, you can move a batch job up to the first position in the holding queue so that it is the first job that gets processed when the system fetches the next held job from the flex queue.
The Holding status is mentioned in the Summer 14 release notes under the new pilot feature of "Submit More Batch Jobs with Apex Flex Queue". Summer 14 release site: salesforce.com/customer-resources/releases/summer14.