Artifacts are various relics, edifices, tools, gear, gadgets, devices, and baubles, often charged with lasting enchantments by wizards of old. is an example of an artifact.
Artifacts have an artifact frame on their card, and typically do not require threshold. For example, or . Artifact subtypes include Armor, Device, Document, Instrument, Potion, Relic, and Weapon, which have no special game rules, though other cards may reference them. There are two special artifact subtypes, Automaton and Monument, which have special rules, described below.
Artifacts have characteristics, specifically artifact characteristics, and are one of the six card types in the game.
By default, any non-Monument, non-Automaton artifact can be carried by a unit. If such an artifact is not carried, then it is not controlled by anyone. If such an artifact is carried, then it's controlled by the bearer's controller.
The "Casting Artifacts" entry has details on how to cast artifact spells.