A tuner is a device that is used to determine whether a musical instrument is producing sound at the correct pitch, and helps to bring the instrument into tune when it isn't.
A tuner is a device that is used to determine whether a musical instrument is producing sound at the correct pitch, and helps to bring the instrument into tune when it isn't.
While a simple tuning fork merely produces a particular pitch by which to compare, an electronic tuner measures the pitch the instrument is making, and indicates whether it is above (sharp) or below (flat) a desired pitch.
Some tuners are designed for particular instruments.
Questions on the different types of tuners and how to use them effectively are on topic with this tag.
This tag should not be confused for the distinct but related tuning tag, which is used for the physical act of adjusting the tuning, and for the particular system of pitches used by an instrument.