"Linking" is already used to describe both object file linking (which is unrelated to deep linking) and html anchor linking (which is related to but different from mobile app deep linking). If you want a generic term, one can of course use the word linking to refer to deep linking, but it's often valuable to have a more specialized term that distinguishes links to functionality in mobile apps from links to anchors in web pages.

Deep linking isn't "linking" between websites or SPAs, which is why you are having a hard time understanding it.

Deep linking refers to linking between a website, into a specific location of a native mobile application, or linking between two mobile applications.

It requires more than a static http link between sites