A tuner is a device or person that adjusts something to make it work at exactly the right setting.

The most common type is a musical tuner, which helps musicians adjust their instruments so they produce the correct pitch. A piano tuner visits homes and concert halls to tighten or loosen the strings inside a piano until each note sounds precisely right. Guitarists often use small electronic tuners that listen to each string and show whether it's too high, too low, or perfectly in tune. Without proper tuning, even expensive instruments can sound terrible, which is why professional orchestras have someone play a single note before concerts so all the musicians can tune together.

The word also applies to radio and television tuners, which adjust to receive specific channels or stations. When you turn the dial on an old radio, you're using a tuner to find the exact frequency where your favorite station broadcasts.

Car enthusiasts talk about engine tuners: mechanics who adjust engines for better performance. A skilled tuner might modify the fuel mixture, timing, or other settings to make a car faster or more efficient.