A form of protection separating cycling (or walking) from motor traffic, that involves separating these modes physically.
The Ranty Highwayman definition describes spatial protection as
A "catch-all" term to describe how space can be used to protect people walking or cycling. For example, footways are a type of spatial protection in that clear space is provided within which people should be able to walk in safety (I say should as people still drive on the footway). Spatial protection can include elements of parking control, bollards, kerbs, barriers and so on. Good levels of spatial protection will be those features which are continuous and don't remove protection where it is needed