The Workstream Lead manages a work package within a project.
A work package is a piece of the project scope; a convenient lump of the project able to be completed or managed by a single party, a work stream is the collection of activities.
If we consider a cake as being a work package, the work stream is the grower, shopper, the cook. One can generally perceive this as an interchangeable word with ‘process’ or ‘activity’. The activity/ workstream/ process lead has responsibility for this.
Similar to the Stage Manager, the Workstream Lead could be an expert in the particular workpackage they are managing, for example, the test phase (or test workpackage) of the project may be managed by the Workstream Lead.