Spaces enable you to organize your Accompa system. A space in Accompa is a collection of requirements (and related artifacts such as use cases, test cases, issues, etc) for a specific project, or other specific entities.
For example, an Accompa space could be:
You can define which users have access to a space, which objects & fields are included in a space, and more.
Here's a video that gives an overview of spaces in Accompa: