Just to expand on that good explanation,
The people involved in The Society for Creative Anachronism (pronounced SCA) form groups or 'guilds' to recreate whatever aspect of medieval life interests them. Some people like to fight with swords (non-lethal of course), some like to brew ale and mead, some like to sew, etc.
SCA is nation wide but to the best of my knowledge, it is a loose confederation of individuals with no "Business" ties. As BG mentioned, they've divided the US into "Kingdoms" and "Baronies" and each area elects its own "rulers" from among their membership.
The link is totally safe and very interesting if you've never encounter SCA folk before
