Tone of voice
Tone of voice is how a brand's constant voice adapts to a specific context: the same personality expressed with a different mood depending on the audience, channel, and situation.
Tone is the situational layer on top of voice. Voice is constant; tone shifts. A warm, confident brand keeps that personality everywhere but sounds celebratory in a launch, calm and accountable in an outage apology, and efficient in a password-reset email.
Getting the distinction right is what stops a writer from being chirpy in an apology or robotic in a celebration. Document your voice once, then add a short tone matrix mapping common situations to the right mood.
Learn more in brand voice vs. tone of voice, or try the free tone of voice generator.