Scholars define a Holde as any bounded place where the rules of an "other realm" hold sway, but are still of this world. There are normally boundry markers of some kind. Plylon or stella are the normal markers, but glyph disk, glowing stones, or an inset stone line are possible.
Inside the defined area, a "hybrid space". Unlike a regio, where two realms overlap and cross over is possible, Holdes are "bubbles" where the rules and powers of another realm have sway. They do not surplant the rules of the world, but add their influences to them.
These are created any number of ways. The most common is to bind a regio, cutting it off from its other realm. The realm energy remaining is trapped and creates the Holde. The next most common is for someone to summon the energy to the world and bind it with the stella. Any one of a dozen combinations of ley lines, charms, rituals, and synchronicity, random or intended can create a Holde for a time. Those can be made forever stable by creating boundry markers.
There are six kinds of Holdes:
Divine Holde: This is a celestial Holde associated with a Deity. These are normally small in size and temporary in nature. They are normally made by a devout follower for a specific purpose. A summoning circle is a very small, fragile holde.
Dark Holde: This is Holde where Deamons hold sway. These are often confused with Divine Holdes of an infernal nature. They are seperate as Deamons, while often alligned with infernal deities, have independent existances. Deamons are beings from various "places" and realms, rather than full sphere. Deamons are energy forms, related to fey, but who can feed of energies generated by mortals (souls, emotions, etc) to enhance their personal power. They travel from their realms to spheres/ worlds to gain power. Dark Holdes are encampments for them, where their own rules hold sway.
Fey Holde: This is a Holde related to the Shidhe and Fey beings. Both the Fey and Fey Hunters will bind holdes (for different reasons of course). They are used as embassies and stop overs, as well as homes away from homes, by the Fey. In a holde, their glamours function as if they were in a fey place or realm.
Grey Holde: This is a Holde that supports the spirit and dead. In these Holdes, the spirits have stronger abilities to effect the material world. It is seldome that these Holdes are created intentionally. They are normally temporary or accidental in nature. The Great City of Merideth is said to be a Holde, but many scholars consider it a regio.
Mythic Holde: This is a Holde where some mythic time or story holds sway. It is a bubble where these mythic events can manifest and replay in endless variation. The Barrows of The First Men are Mythic Holdes.
Time Holde: This is a subtype of the Mythic Holde where a given era is preserved. This bubble of time keeps the ethos of a place alive until the Holde is destroyed. This is a bar that forever lives in the Jazz Age in San Francisco that is a Holde.