Health is the character attribute used to soak up damage from melee and magical attacks. The more Health you have, the hardier you are, and (all else being equal) the more likely you are to survive combat. The Health pool is represented by an orange bar below the name of your character in the default user interface.
Health is regained over time. Food increases the regeneration rate of the Health pool, but only out of combat. Various items, spells and Dirge songs can also increase the regeneration rate, even within combat. Healing spells can add large amounts of Health to the Health pool instantly.