A value proposition is the clear promise of the core value your product gives the customer. It answers one question: why should the customer choose you and not a competitor? A good value proposition isn't a vague slogan — it combines a specific problem, a specific audience, and a specific result.
Don't confuse it with the offer. The value proposition is the broad strategic promise (why you're valuable). The offer is the concrete sales form of that promise (what exactly you're offering right now, on what terms).
How to write a strong value proposition
The formula is simple: [for whom] + [which problem] + [via what unique method] + [what measurable result]. For example: "For growth-stage IT companies — we tie marketing and sales into one system and deliver sales-ready leads, not subscribers."
The value proposition echoes everywhere from the landing-page headline to the ad copy. If it's vague, all of the marketing becomes vague.