Each workflow consists of a sequence of work items which represent the individual steps of a workflow definition at the runtime of the workflow. A Work item is the task instance that is performed as a single workflow step.
For e.g Check that there are no spare computers available in the company.
These work items are executed by human agents ("dialog work items") or by the system in the background ("background work items"). A Work Item is the runtime object of a workflow or of a single-step task.You can execute dialog work items with the inbox (transaction SBWP).
Each workflow and single-step task started is assigned a unique number known as the work item ID. The work item cannot be used to notify several users. when a work item is processed by one of the recipients it will automatically disappear from all the other inboxes. So you can see that a work item is unsuitable for notifying several users.