A xylophone is a long musical instrument with wooden bars that is played by hitting it with small hammer-like mallets.
The xylo- part of this word comes from the Greek for wood — xylon — and clues us in to what gives this instrument its unique sound: the graduated bars representing tones of the scale. A related word in English is xylem, the tissue that forms the woody part of plants. The phone part means "a sound" in Greek. If your instrument has metal bars instead of wooden ones, it is more likely to be a glockenspiel, instead of a xylophone.