Basic, Agile, Scrum, and CMMI
The default processes differ mainly in the work item types (WITs) they provide for planning and tracking work.
Basic is the most lightweight and is in a selective Preview. Scrum is the next most light-weight. Agile supports many Agile method terms, and CMMI, which stands for Capability Maturity Model Integration, provides the most support for formal processes and change management.