The resource breakdown structure (RBS) is created during the estimate activity resources process. It is "a hierarchical representation of resources by category and type." A related output is the activity resource requirements which identifies the resources for each activity. While the activity resource requirements tie the resources to specific activities, the resource breakdown structure organizes similar activities together. A skill may be required by more than one activity, and this organization can let you know how long some staff members will be needed. It could also support consolidation of supply ordering and volume discounts. This information is then used in the estimate activity durations and develop schedule processes (in the PMI structure).
See section 220.127.116.11 of the PMBOK.
The RBS usually includes human resources (organized by skill or organization). It also includes other resources such as equipment, locations, and supplies.
- Wikipedia on resource breakdown structure
- MyPM article Resource Breakdown Structure Template has information about creating the RBS and templates.