Short version: Brand strategy is the set of decisions that define what a brand stands for, who it serves, and how it should compete.
It connects audience insight, market context, positioning, value proposition, personality, messaging, proof, and long-term business goals. Without strategy, branding can become a collection of attractive assets with no clear reason behind them. With strategy, the brand has a direction that can guide naming, identity, website copy, campaigns, content, sales conversations, and product decisions.
Good brand strategy is specific enough to make choices easier. It should clarify who the brand is not for, what problem it wants to own, why customers should care, and how the brand should sound and behave. It also needs to stay connected to reality: the company must be able to deliver the promise it makes.
Related terms: positioning, value proposition, and buyer persona.