There are hundreds and hundreds of NDIS line items. In the Price Guide and in NDIS Plans, these are grouped into Support Categories (e.g. Assistance with Social & Community Participation) and Support Purposes (e.g. Core).
Registration Groups are a different way of grouping the hundreds of line items. Rather than grouping by life domain, Registration Groups are based the skills and compliance obligations required to deliver the support. The number of each registration group is reflected in the third set of numbers in a line item number.