I think that nowadays this term is rather used to describe preparation of the bridge to resist any terrorist attack attempts. This will include placing of the shields around the cables or stays (spaced armor concept), or making it difficult to access some vital points, or placing video monitoring or motion detectors in specific areas.
During the design of the new bridge, some of these features could be easily incorporated in the general concept.
I've noted some bridge hardening projects already completed, or nearing completion in the NYC metro area.