What are the three building blocks of Flow Orchestration?

Flow Orchestration structures complex, multi-user business processes by organizing work into Stages and Steps, with Work Items representing the executable assignments created for interactive steps. A Stage groups related work into a logical phase and controls when the orchestration can progress to the next phase. Steps reside within stages and can execute sequentially or concurrently depending on the process design. Salesforce supports interactive, background, and MuleSoft steps.

When an interactive step becomes active, Salesforce creates an Orchestration Work Item and assigns it to the designated user, group, or queue. The assignee completes the associated Screen Flow through the Orchestration Work Guide. Work Items therefore operationalize the human work represented by interactive steps and provide assignment, completion, and tracking information.

Current Salesforce terminology formally describes Stages and Steps as the building blocks of an orchestration, while Work Items are generated during orchestration runtime. The terminology in this question uses the broader architecture in which Steps, Stages, and Work Items constitute the three operational elements being tested. Processes and Blocks are not defined Flow Orchestration structural elements.