Library /sys$common/syshlp/pca$help.hlb DEFINE, /COMMAND, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The DEFINE/COMMAND command associates a symbol name with a PCA
    command string. The command string consists of one or more PCA
    commands separated by semicolons, and must end with a partial or
    full PCA command. When the symbol name appears at the start of a
    subsequent PCA command, it is replaced by the command string. The
    resulting string is parsed and executed by PCA. DEFINE/COMMAND
    thus gives you the same command abbreviation capability as the
    symbol assignment statement (symbol-name := command-string) in
    DCL. The command string may contain previously defined commands,
    when those symbols translate directly into PCA commands. (PCA
    supports one level of symbol translation.)

    To display the current symbol definitions created by DEFINE
    /COMMAND, use the SHOW SYMBOL/DEFINED command.