Definition of OS/2 in The Network Encyclopedia.
What is OS/2?
OS/2 is a 32-bit operating system originally developed by IBM and Microsoft as a replacement for MS-DOS. IBM later extended OS/2 to include both server and desktop versions. IBM’s current line of OS/2 software includes the OS/2 Warp Server, the OS/2 Advanced Warp Server, and the OS/2 Warp 4 client.

OS/2 Warp in its various forms is a 32-bit preemptive multitasking operating system that supports application, file and print, groupware, and Web server configurations as well as desktop workstations. OS/2 Warp Server includes symmetric multiprocessing support and clustering technologies for high-availability server environments.
OS/2 Warp Server supports most common networking protocols and all types of clients, including Microsoft Windows, Macintosh, and AIX clients.
OS/2 subsystem
OS/2 subsystem is a component of the Microsoft Windows NT operating system running in user mode that supports the running of OS/2 1. x text-based applications on Windows NT. The OS/2 subsystem is rarely used and is not compatible with the OS/2 Presentation Manager graphical user interface.
In Windows 2000, OS/2 subsystem can be used only on a local computer, and can’t be used from a Terminal Server client computer