Armor
Armor (or "armour" as wasteful British typesetters would have you call it) is simply protective clothing that can provide a defense against melee weapons and missiles. It is not uncommon for armor to also protect against physical (or "elemental") spell attacks, such as a fire bolt or cold ball. Armor frequently inhibits spell-casting in some way and may provide some defense against non-physical spell attacks.
Armor in roguelikes usually is worn in parts, typically including most of the following:
* Helmet or cap * Body armor * Cloak * Boots or shoes * Gloves or gauntlets * Shield * Trousers
In a science fiction roguelike, armor may provide environmental protection against toxic gasses or vacuum. It may have built-in weapons or other devices. It might have other features.
In a fantasy roguelike, armor is often magical, not only enhancing basic protection, but offering resistance to various elements or granting various powers.