Sub-process

Is an activity whose internal details have been modeled using activities, gateways, events and sequence flows. The element has a thin border.

 Reusable Sub-process

Identifies a point in the process where a pre-defined process is used. A reusable sub-process is called a Call Activity in BPMN.  The element has a thick border.

 Event Sub-process

A Sub-process is defined as an Event Sub-process when it is triggered by an event. An Event Sub-Process is not part of the normal flow of its parent Process—there are no incoming or outgoing Sequence Flows.

 Transaction

Is a Sub-process whose behavior is controlled through a transaction protocol. It includes the three basic outcomes of a transaction: Successful Completion, Failed Completion and Cancel Intermediate Event.

 Ad-Hoc sub-process

Is a group of activities that has no REQUIRED sequence relationships. A set of activities can be defined, but the sequence and number of performances for the activities is determined by the resources of the activities.

 Standard loop

Sub-processes may be repeated sequentially, behaving like a loop. This feature defines a looping behavior based on a Boolean condition. The activity will loop as long as the Boolean condition is true.

 Multi-Instance loop

Sub-processes may be repeated sequentially, behaving like a loop.  The Multi-instance Loop iterates a predetermined number of times. The iterations occur sequentially or in parallel (simultaneously).