The Task [task] table is a special table in ServiceNow that holds records where work is done. It is a base system table, and can be extended by custom tables meant to hold task-like records. It is already the base table for various task types in ServiceNow, such as Incident [incident]. Like any base system table that's meant to be extended, the task table contains a number of fields that are useful for task records and the work that's done in them. For example, the need to assign a task is almost universal among tasks of all types, so the Assigned to [assigned_to] and Assignment Group [assignment_group] fields exists on the base task table.
Note
A base table is a table in ServiceNow that is extended by other tables, but which does not, itself, extend any other table. Recall that extending a table means inheriting its fields and some of its business logic.
The task table (or rather, tables that extend the task table) also includes task-specific functionality built...