The resource histogram is a tool that is often used by the project management team and or as a means of providing a visual representation to the team and to all of those interested parties. Specifically speaking, the resource histogram is specifically a bar chart that is used for the purposes of displaying the specific amounts of time that a particular resource is scheduled to be worked on over a predetermined and specific time period. Resource histograms may also contain the comparative feature of resource availability, used for comparison on for purposes of contrast. Resource histograms are indeed handy tools to utilize for the project management team and or the project management team leader because they allow a quick and easy single page view of exactly what resources are available, what resources are being utilized at the present time (or at whatever time the project management team and of project management team leader is seeking information on), and how long those resources are expected to be tied up.
This term is defined in the 3rd and the 4th edition of the PMBOK.