It's half the length of a full sentence. A half rest is located directly above the middle line on a five-line musical staff. It indicates that no note should be played in that space. The term "half rest" can also refer to an extended rest during a performance or recording. Such a rest may last for several measures or even longer. Half rests are used to indicate that nothing should be played in order not to interfere with the melody or accompaniment. They are therefore useful for showing changes in harmony or rhythm. A half rest can be represented musically by placing a dot above the staff inside the space where it should be played. This is sometimes called a "half stop". Although a half rest is only half as long as a full rest, it can have a considerable impact on the music. For example, if nothing is played during a half rest, it will usually signal a change in some aspect of the composition or arrangement. Half rests appear frequently in classical music and often indicate a change of key.