A radio is an electronic device that receives radio waves transmitted by radio stations and converts them into audible sound. Radios come in various types, including portable, tabletop, and car radios, and can receive AM (amplitude modulation) and FM (frequency modulation) signals. AM radio is known for its long-range signal and ability to penetrate buildings, while FM radio offers higher quality sound and a wider range of frequencies. Radios typically have a tuner that allows users to select different radio stations, and many also have other features such as a clock, alarm, and auxiliary input for connecting external devices. Radios are commonly used for listening to music, news, and talk shows, and have been a staple of mass communication and entertainment since their invention in the early 20th century.