A unique selling proposition is the specific, defensible reason a customer should choose your business over the direct alternatives available to them — not a general quality claim, but a concrete point of difference.
A genuine USP is something a direct competitor couldn't honestly claim in the same way — "we care about quality" isn't a USP, because virtually every competitor claims the same thing. "We're the only local option offering same-day delivery" is, because it's specific and verifiable.
A clear USP should inform brand messaging directly — if it isn't showing up somewhere in your website copy, sales materials or elevator pitch, it isn't doing the work it's meant to do.