I have a taxonomy vocabulary "categories", and decide that one of the terms should no longer be used (because I introduced another field which covers this information).
I could delete the term, but then some existing content would no longer have a category.
What I would like is to "deprecate" the term, such that
- existing content can continue to reference the term.
- the term is still visible in things like search facets.
- the term can no longer be assigned in a term reference field.
- (optional) editing an existing node which references the old term will fail form validation on save, and force to change the term.