Brand positioning is how a business defines what it is uniquely good at, for whom, and against what customers would use instead, so the right buyers see it quickly.
A neighbourhood physiotherapy clinic competes with hospital departments and generic gyms. It positions itself around one thing: recovery after sports injuries, for amateur runners and footballers, with same-week appointments. Its alternatives, its strength, its value, its customer and its category are now clear in one sentence.
Positioning decides how people file you in their heads: what you are, who you are for and why you instead of the alternative. April Dunford, in Obviously Awesome, frames it as defining how your offering is uniquely good at delivering something a well-defined set of customers care about a lot. In her method it is built from a few components: the competitive alternatives customers would use if you did not exist, your unique attributes, the value those attributes create, the customers who care most about that value, and the market category that makes all of it easy to understand.
Her point, which matches what we see, is that positioning is not a tagline. It is the set of decisions that the website, ads, sales calls and pricing all depend on. Without it, each of them improvises.
Clear positioning also makes content and ads sharper: BridgeE begins branding work here, before design.