Crystal radio, also known as crystal set, is a device that is used for creating an electronic circuit that can receive radio waves without any external power. There are several synonyms that can be used instead of crystal radio, including galena radio, cat's whisker radio, and crystal detector. Galena radio refers to the use of galena (a mineral) as the detector element in the circuit. Cat's whisker radio refers to the point-contact diode used in early radio receivers, which had a small wire that was called a "cat's whisker." Finally, crystal detector is a generic term for any device that uses a crystal as a detector element to demodulate radio waves.