A six string guitar with a hollow wooden body. Modern day Classical guitars typically have nylon strings and differ from their electric and acoustic cousin mostly in the music that they play. Classical guitars are also often played using a special technique where individual strings are plucked with the fingernails as opposed to strumming all six strings together.
Electric guitars typically have six (sometimes twelve) metal strings that run over an electric pickup that sends the sound projects the sound through a separate amplifier. Acoustic guitars, much like classical guitars, are not electronically amplified, but still have metal strings like their electric cousins. Electric and acoustic guitars are typically used in popular styles like jazz and rock and roll, as opposed to the classical music typically played on classical guitars.