Hard res or hard rez is a term used to describe any resurrect skill that does not require a morale boost or exit from the explorable area in order to be reused. Resurrection Signet and Sunspear Rebirth Signet are the only resurrection skills that do not fit the "hard res" criteria, and are sometimes referred to as soft rezzes or sigs.
Hard res skills, especially Resurrection Chant, are often combined with Glyph of Sacrifice or Fast Casting to produce an "instant res" which can bring any player to full health instantly.