Brand voice
The consistent way a brand sounds in writing, defined concretely enough that two different people produce the same tone.
Adjectives do not do this job. “Friendly, professional, approachable” describes almost every brand on the internet and helps nobody write a caption. A usable voice is written as rules and as pairs: this, not that.
The useful form is short and specific. Which words are ours and which are banned. Whether we use exclamation marks. Whether a complaint gets an apology or a fix. How formal the reply to a stranger is.
It matters most where nobody is looking: the reply to a complaint at nine at night, the caption written in a hurry between two other jobs. That is where an account either sounds like itself or like whoever happened to be holding the phone.