Omnis are groups of adepts.  Omnis can be guilds, churches, orders, or just groups of scholars or friends with a common purpose or philosophy.
Geoza is home to many Omnis, from divinely inspired temples and orders of holy warriors to guilds of alchemists or academies that train new adepts.  Any organization of aedpts is an Omni, regardless of its specific form, purpose, or philosophy.
Note: although psychics aren't technically adepts, organizations of psychics, whether or not such organizations also include adepts, are classed as Omnis.