Definition:
Parallel development occurs when there is a need for separate development paths to diverge from a common starting point, so that there is no longer a single “latest and greatest” version. Such characteristics determine how the object version is evaluated during an update. The properties that distinguish parallel object versions from each other are called parallel development properties.
Further Reading:
Book: Instant Parallel Processing with Gearman Paperback – Import, 26 Jul 2013 by John Ewart