Rest is class of mechanic that replenishes stats(usually primary stats such as HP/Mana) out of combat.
While in combat, regeneration is usually limited.
A.Idling rest, character remains stationary for N seconds, then his stats are recharged quickly.

B.Mode: characters enter a state(e.g.meditation/sleep) and this starts regeneration, if interrupted regen stops.

C.Instant bonus: always-on regen is boosted while not in combat.