Free work breakdown structure. A WBS is a tool used in project management to divide a project into smaller, more manageable parts. It is a hierarchical representation of the work that needs to be done to complete a project. The WBS is often displayed in the form of a tree structure, with the project at the top level and the individual tasks and subtasks arranged in levels below. Each task in the WBS is assigned a unique ID and is defined in enough detail to allow the team to understand what needs to be done.