In Jewish folklore, a golem is an artificial being made from inanimate matter, traditionally clay or mud, which is then animated by supernatural means. The resulting entity is physically robust and can be directed to perform work, but is usually not fully sapient; lacking both initiative and common sense. Thus its instructions must be carefully worded, lest certain mishaps ensue. Essentially, a magical, pre-industrial robot.
In modern fantasy, a wider range of base materials can be used, with the hardness/toughness of the material serving as an indicator of the golem's strength (e.g. a stone golem is stronger than a mud golem, and an iron golem is stronger still.) This is extremely common in RPGs. Golems may even be depicted as intelligent, although a tendency towards being either dim-witted, subservient or both remains.