From The Heretic Knowledge Vault
Wards are used to guard an area or object. They can be either Spell or Magic Object. Sarine used (or at least offered to use) one here to keep scavengers away from some bodies that Jon had some strong feelings about. Sarine used one later to keep Sara from pre-empting before their duel (and to give Sara a not-very-subtle hint about the perils of hand-to-hand combat against someone who's not only a skilled fighter but also a potent spellcaster).
While wards can be either a spell or a spelled object, only the spell version has been used in the story, thus far. We don't know exactly what happens to the transgressor who sets one off, but it's probably messy. However, the ward used by Sarine against Sara didn't do too much to the latter, possibly because she just barely touched it.
Not to be confused with a magical Lock, which just makes it hard/impossible to open the locked thing, rather than zapping the opener with magical energy if he/she tries -- probably. The cellblock where the elves stashed Meji and Ellis after abducting them probably incorporates wards of some kind, since they'd otherwise be trivial for a magic-using prisoner to get out of. However, all that we've seen there so far are the actual locks.