A "context" allows you to access different workspaces of content. You may have one or more contexts.
The size, complexity, or sheer quantity of organizations to whom you are associated may lead you to belong to an item bank via multiple contexts/workspaces.
In the diagram above, User may access item bank C via Publisher 2, and banks A, B, and C via Publisher 1. In a real-world scenario, Publisher 2 may have leased Bank C to Publisher 1 and granted Publisher 1 read-only access to Bank C, while Publisher A has full access to the same bank. If you attempt to access Bank C via Publisher 1 to edit an item, you may be confused as to why you are not granted access to the editor.
Contexts (or "workspaces") are helpful when a single user has different levels of access. Before attempting to access an item, assessment, resource, etc., be sure your context is set properly.