Base plans are plans that act as templates for other plans. The plans created from base plans are called derived plans.
When a plan is derived from a base plan, changes to the base plan also change the derived plan for options that are inherited. For example, if you change the RPO (recovery point objective) from 4 hours to 10 hours in a base plan, the RPOs for all of the plans inheriting RPO from that base plan are changed to 10 hours.
Note: If you use a plan as a base plan, then do not delete the snapshot copy added to the plan as it prevents you from creating new plans using the base plan.