Giusto
Exact, in the right tempo.
What it means
Giusto means in Italian “right, appropriate, exact.” As a musical instruction it asks that the tempo be kept exactly — without the liberties that are allowed or even desired elsewhere. The word thus stands in contrast to rubato and to all markings that allow stretching and pressing.
Two readings are in use. The first understands giusto as a call for metric strictness: strictly in time, without wavering. The second reads it as “in the appropriate tempo,” that is, in that tempo which corresponds to the character of the piece — for a march the march tempo, for a dance the dance tempo. Which reading applies depends on the context; often both are meant at once.
As an addition to a tempo word, giusto restricts its latitude, for instance in Allegro giusto. On its own the phrase tempo giusto usually stands.
In the notation
The word is written in italics above the staff, either as an addition after a tempo word or in the combination tempo giusto as an independent marking. It can also appear after a free section and then marks the return to regulated tempo — comparable to a tempo but with the additional hint of strictness.
Musical use
The marking is used where there is a danger of too free a conception: in dance-like movements whose metre is sustaining, after cadenzas and recitative-like sections, and in music that comes from a function of use and whose pulse must therefore remain reliable. In the music of the twentieth century giusto occasionally stands in contrast to neighbouring sections with free rhythm.
Performance practice
Take the instruction as a renunciation of rubato: shape through dynamics, articulation, and tone colour instead of through changes of tempo. Count along and check occasionally with the metronome whether you yield unnoticed at phrase ends — it happens most often there. Take care that strictness does not mean rigidity: the metric stresses may and should remain audible. And fix the tempo before the first note, for a tempo kept exactly cannot be corrected later.