There are two alternative meanings to this phrase

A windows manager/desktop environment from Sun. No longer common, so perhaps should be referred to as Uncommon Desktop Environment.

A concept in government (and possibly corporate, though I've not encountered it there) of OS consistency across all machines. This is the software complement to Managed Workstation. The standard is to require all workstations to run the same OS/version/patchlevel and a core set of applications that are identical. Job specific applications are added after the machine is imaged, but users are not able to install anything else without IT intervention. The goal is to lower support costs and ensure stability.