This section should define what's in the scope of the project, as well as what is beyond the scope. You should provide a rationale for why the scope is defined in a particular way, especially when writing about things that won't make the cut.
This section should also cover the high-level functional and nonfunctional requirements, but details should go into the subsequent sections of the document. If you're familiar with Agile practices, just describe epics and bigger user stories here.
If you or your stakeholders have any assumptions regarding the scope, you should mention those here. If the scope is subject to change due to any issues or risks, you should also write some words about it, and similarly for any trade-offs you had to make.
