A Workbook is a collection of Views. When publishing to Tableau Server, you can elect to display one or more of the Views in a Workbook (assuming you have more than 1 worksheet/dashboard). Any Views you select to display are put out on the Server and can be accessed by a specific url from within your network.
You can also assign your Workbooks and Views to "Projects" on Tableau Server. I think these are the highest tier of organization. (Workbooks within Projects, Views within Workbooks)
For instance, a Workbook you publish under "Project 246 - Survey data" would show up as 1 Workbook as many Views as you expose from the Workbook and all would appear under the "Project 246 - Survey data."