GPO
Short for Group Policy Object, GPO is a computer or groups of computers on a network that have a Group policy applied. A GPO can be edited using the gpedit (easily accessed by running: gpedit.msc) or in Windows XP Professional Windows 2003 through the Group Policy Management Console (GPMC) tool available here. Below is a picture of what the Group Policy window may look like in Windows XP.
Also see: Active directory, Group policy, Security definitions