Product
A product is software finished to the point that people outside the team can use it, and usually pay for it.
What it tells you about a developer
A developer who has shipped a product, even a small one, has dealt with real users, edge cases, and long-term maintenance. That experience transfers across every stack.
Code that runs on a developer’s laptop is a long way from a product. The gap gets filled by deployment, accounts and payments, design, documentation, support, and handling every way a stranger can misuse the thing. Turning code into a product takes more roles than engineering, and the engineering itself shifts from making it work to making it dependable.