Your specification can be designated along those lines:
Describe the entity where the project is being launched and the context in which the project will take place
Describe all internal and external stakeholders involved in the project
Define precise objectives of the project
Divide the project to access the best partners by sub-project
Plan the project in a structured way by describing all the steps of creation, integration, development, acceptance, writing, and then launch, taking into account validation deadlines, vacations, bottlenecks concerning some teams or tasks
Describe the ecosystem around the project in order to determine the cost
Structuring the different perimeters:
Functional => Describe all the awaited features
Non-functional => Describe the specifications, governances, conformities, restrictions, etc.