From Michael Pöttgen <firstname.lastname@example.org>:
The ‘Windows Font Mapping’ article says that FT_WinFNT_ID_OEM is used for the charset of vector fonts, like ‘modern.fon’, ‘roman.fon’, and ‘script.fon’ on Windows.
The ‘CreateFont’ documentation says: The FT_WinFNT_ID_OEM value specifies a character set that is operating-system dependent.
The ‘IFIMETRICS’ documentation from the ‘Windows Driver Development Kit’ says: This font supports an OEM-specific character set. The OEM character set is system dependent.
In general OEM, as opposed to ANSI (i.e., cp1252), denotes the second default codepage that most international versions of Windows have. It is one of the OEM codepages from
and is used for the ‘DOS boxes’, to support legacy applications. A German Windows version for example usually uses ANSI codepage 1252 and OEM codepage 850.