What is this option in my BIOS for?

[Superman]

There's an option in my BIOS menu that reads, "OS Select For DRAM > 64MB." The manual has this to say about it, "A choice other than Non-OS2 is only used for OS2 systems with memory exceeding 64MB. The Choices: Non-OS2 (default), OS2."

Does "OS2" refer to computers with a second operating system? I can't find the answer.

[Mr Bean]

OS2 refers to an old time operating system. A very old time operating system. You don't have OS2.
*Edit Wiki quote

OS/2 is a computer operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2," because it was introduced as part of the same generation change release as IBM's "Personal System/2 (PS/2)" line of second-generation personal computers. OS/2 is no longer marketed by IBM, and IBM standard support for OS/2 was discontinued on 31 December 2006.[1] Currently, Serenity Systems sells OS/2 under the brand name eComStation.

OS/2 was intended as a protected mode successor of PC-DOS. Notably, basic system calls were modeled after MS-DOS calls; their names even started with "Dos" and it was possible to create "Family Mode" applications: text mode applications that could work on both systems.[2] Because of this heritage, OS/2 shares similarities with Unix, Xenix, and Windows in many ways.

[Superman]

Woot! Thanks for the help.

[Marcus Aurelius]

OS2 refers to an old time operating system. A very old time operating system. You don't have OS2.

Calling it very old time OS is an exaggeration (and not a small one either). The last retail version was the 4.0 Merlin released in 1996 and the last version released by IBM was 4.52 in 2002. So, it's essentially no older than Windows 9x, even if the first version was released in the 1980's.

By the way, the BIOS setting OP asked about applies only to OS/2 version 2.x, so it has been outdated for more than 10 years (3.0 was released already in 1994). There is lots of old holdover stuff like that in the IBM AT compatible BIOS, which is one of the reasons why it sucks badly.