Unison means everyone doing the same thing at exactly the same time. When a class recites the Pledge of Allegiance in unison, every student speaks the same words together, their voices blending into one. When dancers move in unison, they all perform the same steps at the same moment, creating a powerful visual effect.

The word comes from music, where singing in unison means everyone sings the same notes at the same pitch, as opposed to harmony, where different people sing different notes that sound good together. A choir singing in unison produces one unified sound, while a choir singing in harmony creates a richer, layered effect.

Moments in unison can be striking because they show coordination and unity. When thousands of fans at a stadium chant in unison, the sound becomes thunderous and exciting. When an entire orchestra plays a phrase in unison, the music feels especially powerful and emphatic.

You can use the phrase in perfect unison when the timing is especially precise, or say people did something in unison to emphasize how they all acted together without planning it, like when a whole classroom groans in unison after hearing about a surprise quiz.