BPMN 2.0 processes can be used and reused as Call Activities, read more in the article Call Activities

How to enable a process for reusing

1. Open the Process Settings for the desired process

2. Click on the tab General and enable the setting Reusable 

The process is now available, both in the Asset Browser and when searching for reusable processes, for other processes to reuse as Call Activities.

When should you use Reusable Processes?

A process that has been configured to be reusable can be added to any other process as a Call Activity. This allows you to link one process to another so that you can create a hierarchical structure of your processes. It also allows you to create one process that can be used by several other processes making it possible to ensure that reusable activities are modeled in a single process and allowing other processes to reuse that one single process.