A task manager is a program used to provide information about the processes and programs running on a computer, as well as the general status of the computer.  It can also be used to terminate processes and programs, as well as change the processes' priority.  Task managers include Windows Task Manager and Activity Monitor on Mac OS X (known as Process Viewer prior to Mac OS X v.10.3). 

To learn more about the Task Manager, and how to properly and effectively use it, click here.