Components of Workflow

Workflow Runtime Engine:  Every running workflow instance is created and maintained by an in-process runtime engine that is commonly referred to as the workflow runtime engine.

Host Process:  When a workflow model is compiled, it can be executed inside any Windows process including console applications, forms-based applications, Windows Services, ASP.NET Web sites, and Web services

Runtime Services:  Each service provides a feature that interacts with system outside the workflow. Runtime Services provide features that interact with the Runtime Engine i.e. Persistence, Tracking, Scheduling

Base Activity Library: Out-of-Box activities and base for custom activities library

Custom Activity Library: Custom Activities derive from Base Activity Library.

Workflow:  Workflow is a set of steps / activities