A work list is the list of tasks for an individual user. A work basket is a task list for a group of users. A router rule will send the work to the appropriate person (work list) or group of people (work basket).
In many business processes, tasks to be performed by human workers are stored in central in-baskets or electronic equivalents of in-baskets. A supervisor reviews the tasks and assigns them to a worker on her team, or workers select an item to work on when they become idle. This approach is called "pulling" work.
In other settings, work is sent directly to workers based on their availability or other criteria such as skills, regions, or customer account number. This is called "pushing" work.
It is a mechanism to create a relationship for an end user to move between applications. You should think of WorkPool as Application. SAE-HRServices-Work represents the Application/ClassGroup or WorkPool. Your Cases or Work are contained in the ClassGroup or part of that WorkPool. A user with access to multiple applications is able to change to a different WorkPool, which will change the focus of the Cases he or she can start to those contained in that WorkPool.