The 4D framework breaks up the product development process into four distinct phases.
The discovery phase is focused on the problem and opportunity space. This includes validating that this is a real customer problem and will meaningfully impact the business with measurable success criteria in place.
Customers experiencing the core value of the product.
Once the problem and opportunity are defined we begin to work on a solution. The design solution can take many forms with varying levels of fidelity ranging from wireframes to functioning prototypes. It's good practice to involve the delivery team in the design phase to vet the feasibility of the design solution.
With the design in hand, the team can then begin to develop and deliver the solution. It's up to the team to determine how to define 'done' and when a solution is ready for customers.
This phase is about measuring the delivered solution and determining if this does solve the customer problem and provide business value. This can be done through qualitative and quantitative measures using the defined success criteria from the Discovery phase.