As with marketing strategy, product strategy should flow from the wider business goals. In a business with digital products and/or services, both marketing and product strategy should be intertwined with a close relationship between the two.
The product strategy should translate the wider business strategy into a high-level plan for how the product can fulfil the objectives of the business. This should incorporate a definition of who the product is being built for (the personas), the vision for how the product will serve the needs of those personas and what the product goals are through its lifecycle.
A good product strategy creates alignment and direction, enabling all those involved with the product (including development, marketing, sales, customer success) to see how their work is contributing towards the achievement of organisational goals.