Share of voice in AI search is the proportion of brand mentions in a category that belong to your brand versus competitors, measured across a tracked set of prompts. If ten brand mentions appear across your prompts and three of them are yours, your share of voice is 30 percent.
It is a competitive metric: it shows how much of the category conversation you own. It is usually reported as an aggregate across the AI platforms you track, which is what distinguishes it from share of model.