The workflow definition is the set of rules that determine the path that the process takes. For example, how a purchase requisition is processed, from the initial request to the creation of the purchase order
A Workflow Instance, which is often simply referred to as the workflow, is a single workflow run. For example, the processing of a single purchase requisition for computers.
The Tasks are the steps in the process, which have to be performed either by people or automatically by the software. For example, to check for the availability of the spare computers in the company.
A Work item is the task instance that is performed as a single workflow step. For example, check that there are no spare computers available in the company.
Agents are the people who process the tasks (via the work items). For example, requisitioner and a member of the purchasing department.
Container is the place where all the data used in the workflow is collected.
Binding is the set of rules that define which data is passed to which part of the process.