If your company has enabled the ERP Integrations tool for one of the supported integrated ERP systems, a sub job is a child project of a parent project. For example, a Commercial High Rise project might have a separate Low Rise Executive Office building as a child project. Many, but not all, of the supported ERP systems utilise this concept.
For companies using the ERP Integrations tool, visit Things to Know About Your ERP Integration to learn if and how your integration supports the use of sub jobs in Procore.