An electric guitar is a type of guitar that uses pickups to convert the vibration of its steel-cored strings into electrical current, which is then amplified.
Some steel-string acoustic guitars are fitted with pickups purely as an alternative to using a separate microphone. They may also be fitted with a piezo-electric pickup under the bridge, attached to the bridge mounting plate, or with a low mass microphone (usually a condenser mic) inside the body of the guitar that will convert the vibrations in the body into electronic signals, or even combinations of these types of pickups, with an integral mixer/preamp/graphic equalizer. These are called electric acoustic guitars, and are regarded as acoustic guitars rather than electric guitars because the pickups do not produce a signal directly from the vibration of the strings, but rather from the vibration of the guitar top or body. These should not be confused with hollow body electric guitars, which have pickups of the type found on solid body electric guitars.
Some people also refer to it as plug-in acoustic.
Many guitar-making brands, such as Gibson, Takamine, and Fender, for example, have different models of the guitar. Fender titles it "electracoustic", and it has a very distinct body shape, different than most other models. Takamine, though probably not heard of often, makes almost only electric-acoustic guitars. They also make special edition guitars, with beautiful inlays and specail details on the body or the neck of the guitar every year. Some of the artists that design guitars for Takamine include Jon Bon Jovi, Kenny Chesney, Toby Keith, Benji Madden, Joel Madden,and Paul Thomas (the last three names were band members of Good Charlotte) Joe Don Rooney (from Rascal Flats), and Bruce Springsteen.