American Idol's judges, such as Randy Jackson, never seem to get tired of bantering those less-gifted singers with phrases like, "that's a little pitchy."

It turns out that it means exactly what you may have guessed: "Pitchy means out of tune," said Elizabeth Marvin, professor of music theory at the University of Rochester in New York.

Musicians, especially pop singers , typically sing along with instruments that are tuned such that each note corresponds to a frequency, or pitch, Marvin said.

Sound is transmitted in waves, and each note on a music scale differs from the others in the frequency of its waves waves that are closer together have a higher frequency than waves that are spread farther apart.

Wave frequencies can be measured in hertz (Hz), a unit that indicates the number of cycles per second; a 50-Hz wave has a frequency of 50cycle per second.

Each musical note has a unique frequency. For example, the A note is 440 Hz, while G is approximately 784 Hz.

If, while singing, a singer produces sound waves that are slightly above (sharp) or below (flat) the expected pitch, the judges call it "pitchy," Marvin said.

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