An electric guitar is a guitar that uses external amplification in order to be heard at typical performance volumes. The vibration of its strings is converted into electrical signals, which are then converted into sound by loudspeakers. The sound can be electronically altered to achieve the desired timbres.
The electric guitar was introduced in the early 1930's and was first used by jazz guitar players. From around mid-century it became the most important instrument in popular music and served as a major component in the development of rock and roll and many other genres of popular music. It is also being used in some art music.
Electric guitars and acoustic guitars have several important things in common. Both have six strings which are tuned with tuning pegs and both have frets on a long neck. They also have wooden bodies, although those on electric guitars have a very different shape and are usually finished to look like plastic or metal. However, the bodies of acoustic guitars are always hollow while most electric guitar bodies are solid or only partially hollow.