An artifact or artefact is any object or process resulting from human activity. In a broader sense, it may be defined as anything created by any intelligent being, but at the moment our knowledge of intelligent beings consists of one example -- humanity. (Some ethologists, scientists who study animal behavior, may not agree with this assertion; nor would many UFO enthusiasts).
In an archaeological sense, an artifact is any object discarded or lost by a previous human culture, and later recovered by some archaeological endeavor. Prehistoric artifacts might include stone tools such as projectile points, ceramic sherds, or grinding slabs; historic artifacts include objects made of glass, metal, brick, concrete, mortar, ceramic, and the like.
In observational science and particularly signal processing, an artifact is any perceived distortion, error, or addition caused by the instrument of observation (signal processor). For example, a compression artifact is a noticeable error caused by lossy data compression of digital audio or video data. A similar usage applies in printing and graphic design, where an artifact is a visible blemish not present in the original image or plate.
In role-playing games and fantasy literature, an artifact is a magicalal object with some marvelous and alarming power, so great that it cannot be duplicated by any known art allowed by the premises of the fantasy world, and cannot be destroyed by ordinary means. Artifacts often serve as MacGuffins, the central focus of quests to locate, capture, or destroy them. The One Ring of The Lord of the Rings is a typical artifact: alarmingly powerful, of ancient and obscure origin, and almost indestructible.