A similar entry appears in the Wheel of Time Companion confirming the information available in the main story arc.
Artham were ter'angreal that hid the person holding it from the forces of the Shadow, or even the Dark One himself. They were most likely made during the Breaking as Rand says he heard about them during the Age of Legends, but nobody created one, and wonders who finally managed it (AMoL, Ch. 20). Aviendha found one in the cache of Power related items that the Kin had collected along with the Bowl of Winds in Ebou Darm a small dull bladed dagger with a rough hilt of deerhorn wrapped in gold wire (TPoD, Ch. 4) and gave it to Elayne to protect her babes (KoD, Ch. 15). Elayne later gives it to Rand (AMoL, Ch. 10) and he confirms that he is able to get right to the entrance to the Pit of Doom without being sensed (AMoL, Ch. 20)