The workflow widget is categorised as a Useful widget and provides a graphical workflow style display of 'stages' on the dashboard.
Only single select type custom fields can be added into a Workflow widget. A workflow can be generated for any module (Contacts / Opportunities/ Custom objects & etc..). Learn more about adding widgets here.
Once the field is selected, the values attributed to the select field will display as a graphical workflow within the widget.
Click on a workflow icon to drill into the results on the module's list view page.