Intonation (music)
The word "intonation" is used in music to describe whether someone who is playing a musical instrument is playing in tune. This is not used for instruments such as the piano which are tuned already, but for an instrument such as the violin there is a lot of skill and practice needed to play with good intonation (to play well in tune).  A violinist needs to put his or her fingers in exactly the right place on the fingerboard, otherwise the note will be sharp (too high) or flat (too low).  Musicians playing in a group will need to listen to one another so that their tuning (intonation) is good. Players of wind instruments and singers all need to pay careful attention to their intonation.