Forbid items/buildings

From DwarfFortressWiki

Marks every item and building in the selected area as forbidden. Forbidden objects are completely ignored by dwarves and do not contribute to fortress value.

Uses for forbid include:

• Preventing dwarves from trying to retrieve items from an area controlled by hostile monsters
• Forcing dwarves to use specific materials, for example when satisfying a mandate or demand
• Preventing dwarves from moving items that are on fire

Items are automatically marked "Forbidden" when

• reclaiming a fortress.
• they have been dumped in a garbage zone.
• you begin a game in a town – all items in the town are initially forbidden.
• a crossbow bolt is fired and drops on the ground intact.

The opposite of forbid is reclaim, which removes the forbidden status of items.