piano
A piano is a large musical instrument that you play by pressing black and white keys on a keyboard. Most people play a piano with their fingers, but Jerry Lee Lewis played with his fingers, feet, elbows, and, ahem, backside.
guitar
The guitar is a fretted musical instrument that typically has six strings. It is usually held flat against the player’s body and played by strumming or plucking the strings with the dominant hand, while simultaneously pressing selected strings against frets with the fingers of the opposite hand.