Fixed device, or fixed object is a not widely used term that applies to any object that cannot be picked up or moved (is fixed in place) in the game world, but can be interacted with in some way (buys from your character, works like a container, exchanges items, opens or closes, gives a quest, can be read, repairs your items, sells to a character, etc.). The most commonly used object of this type is the mailbox.
Fixed devices are distinguished from spawned objects in that they never appear based on some trigger or disappear after use. They are always present in the game world. Non-interactive, visible parts of the game world might also be called fixed devices, but perhaps more properly, fixed decorations.
- Examples of fixed devices
- Mailboxes, forges, anvils and permanent cooking fires
- In-game books (most of them)
- Doors and levers to open or close them
- Sparklematic 5200
- Buzzbox 323, Buzzbox 411, Buzzbox 525 and Buzzbox 827
- Quest items that do not disappear or change after use and cannot be picked up.
- Various benches, chairs and the like.
Pointers for using (non-mailbox):
in range to use 
out of range