Tuning is a word used to describe the precise pitch of a note sung, or played by a musical instrument. There are three kinds of tuning that are important. The first is relative tuning, which refers to the relationship between different notes sung or played on the same instrument. Next, is the relative tuning between instruments. Third, is absolute tuning, which compares the pitch of a note to a specific frequency (The note “A” might be defined as 440Hz).
When you are playing an instrument (or singing) by yourself, as long as the notes have the right relationship to each other, the music you play will sound in tune. This type of tuning is needed for a melody.
When you play music with other people, it is important that everyone’s tuning matches; so that the music sounds good. As long as everyone is tuned the same, absolute tuning is not essential, although it can make things easier. If you are slightly out of tune with each other, the notes will often sound horrible, and send a shiver down your spine.
When playing in a large group, like an orchestra or concert band, usually a reference pitch is played by a single instrument, and everyone else tunes to that person by ear. Usually, the reference instrument will tune to a reference pitch, often using a tuner app, like Timbre.