The Free On-line Dictionary of Computing (19 January 2023):

Control Program for Microcomputers
CPM
CP/M

    (CP/M) An early microcomputer operating
   system written by Gary Kildall of Digital Research for
   8080 and Zilog Z80-based 8-bit computers.

   Many of CP/M's features and conventions strongly resemble
   those of early DEC operating systems such as TOPS-10,
   OS/8, RSTS and RSX-11.

   CP/M was very popular in the late 1970s and Bill Gates
   suggested using it as the OS for the IBM PC.  IBM wanted
   to own and control the OS completely but could not get Digital
   Research to sign a non-disclosure agreement, which killed the
   deal.  CP/M was virtually wiped out by MS-DOS after the
   release of the IBM PC in 1981.

   The file system of MS-DOS was patterned closely on CP/M's,
   including the use of 8 + 3 (upper case) character file names.
   The first version (MS-DOS 1.0) was even limited to a single
   directory, like CP/M.

   (2020-08-19)


The Jargon File (version 4.4.7, 29 Dec 2003):

CP/M
 /C·P·M/, n.

    [Control Program/Monitor; later retconned to Control Program for
    Microcomputers] An early microcomputer OS written by hacker Gary Kildall
    for 8080- and Z80-based machines, very popular in the late 1970s but
    virtually wiped out by MS-DOS after the release of the IBM PC in 1981.
    Legend has it that Kildall's company blew its chance to write the OS for
    the IBM PC because Kildall decided to spend a day IBM's reps wanted to meet
    with him enjoying the perfect flying weather in his private plane (another
    variant has it that Gary's wife was much more interested in packing her
    suitcases for an upcoming vacation than in clinching a deal with IBM). Many
    of CP/M's features and conventions strongly resemble those of early DEC
    operating systems such as TOPS-10, OS/8, RSTS, and RSX-11. See MS-DOS,
    operating system.