If you do a search in the Pega platform help on "Work-Cover" you will find far more details than I can provide here.

However,  Work- and Work-Cover- are parent classes for work items and cases that are specified in a user's access group and/or the work items/cases that are found in a user's work pool. Additionally, work types that are derived from the Work-Cover- base class are what are referred to when discussing case types.

Hope that helps.

-- Glenn