Microsoft Dynamics 365 December 2016 release (version 8.2) included some significant changes to Dynamics CRM Business Process Flow data model and entities structure.
In the new Model, every time a business process flow is activated, a custom entity is automatically created to store the activated business process flow instances.
Before that, every time you create a business process flow, it is stored in the Workflow entity (https://msdn.microsoft.com/en-gb/library/mt622427.aspx).
The Workflow entity stores the business process flow definition. So once the entity is created, it is always in Draft state and its definition is stored in Workflow entity. XAML property is where the definition is stored and is mandatory/required.
Once you activate a business process flow definition (by changing the state of the corresponding Workflow entity record), a custom entity with the following name is automatically created to store the activated business process flow instances:
More details can be found in this MSDN Article here:
There is also the Process Stages Entity which contains: Step metadata for process stage (Client Data). It also contains stage Category (Qualify, Develop, Propose, etc.) as well as the Stage Name.
Properties represent fields of data stored in the entity. Some properties are read-only.
|clientdata||Edm.String||Description: Step metadata for process stage
Display Name: Client Data
|owningbusinessunit||Edm.Guid||Description: Select the business unit that owns the record.
Display Name: Owning Business Unit
|primaryentitytypecode||Edm.String||Description: Primary entity associated with the stage.
Display Name: Primary Entity
|processstageid||Edm.Guid||Description: Shows the ID of the process stage record.
Display Name: Process Stage
|stagecategory||Edm.Int32||Description: Select the category of the sales process.
0 : Qualify
Display Name: Stage Category
|stagename||Edm.String||Description: Type a name for the process stage.
Display Name: Process Stage Name
|versionnumber||Edm.Int64||Description: Version number of the process stage.
Display Name: Version Number
More information on the ProcessStages entity is here:
Finally, here is a Dynamics Community post with few more information and discussion on this subject: