A spatial anchor is a reference pose used by an AR system to keep digital content associated with a location and orientation in its understanding of the environment.
Think of a reference for placement
After placing a virtual object, the application can relate it to an anchor. As tracking estimates improve, the system updates that reference. This helps manage spatial placement; it is not a physical attachment or a promise of perfect stability.
A museum example
An interpretive object might be positioned beside a display case. The anchor provides a spatial reference for that placement during the experience. Image-based references and room-based references may be managed differently by the chosen AR system.
Does it stay there tomorrow?
Not necessarily. A session anchor may exist only while the current experience is running. Returning to the same location in a later session, or sharing it with another visitor, requires a supported persistence or shared-localisation mechanism.
Questions to ask before commissioning
Ask what happens after closing the browser, changing devices, moving the exhibit or changing the room's lighting. Do not infer persistent or shared anchors from a platform merely supporting AR. Verify those behaviours in the installation conditions.
Related concepts and further reading
Google ARCore: working with anchors
Explore related 3D and spatial concepts
The reference an anchor maintains is a pose: a position and orientation relative to a coordinate system.