The Kingdom of AEthelmearc has three main types of groups listed on its site:

Local groups are our chapters, which are called Baronies, Shires, and Cantons (and a Dominion). Each group has its own slate of officers to run it. It is the members of the local chapters who actually plan and run the events, practices, and other activities for SCA participants.¹

Kingdom guilds are groups of people who have chosen to study a particular skill or area of interest. Membership is usually open to anyone with interest.²

Polling orders require that the Crown consult the Companions regarding potential members.²

1. From https://www.sca.org/what-is-the-sca/

https://web.archive.org/web/20210411002433/http://www.chezirene.com/articles/scagloss.html (originally not on archive.org).