On a SharePoint site’s hidden Workflow History list you might stumble across some strange numbers. The Event Type is used to store a numeric value and below I’ve listed what each means in plain English.
These map to Microsoft.SharePoint.Workflow.SPWorkflowHistoryEventType which contains their values in Visual Studio for developers.
Unfortunately MSDN does not list the numeric values for use by power users to create filtered views in the browser. However, I have them here: