Sub-Processes and Call Activities
A sub-process forms a process that is a part of a bigger process and can contain other tasks, gateways, and events. A sub-process is completely defined inside a parent process.
A call activity references a process that is external to the process definition, whereas the sub-process is embedded within the original process definition. For some cases, it is useful to have a process definition that can be called from other process definitions.
For more details about sub-processes and call activities, see Flowable documentation.