Represents a single compilation unit. You can list the modules
    with the SHOW MODULE command. Each module shown represents a
    single compilation unit - the smallest piece of source that can
    be separately compiled. Even if several of these are compiled at
    once (which is common in languages such as FORTRAN and BASIC),
    each compilation unit appears separately.

    In the query language, SYMBOL=MODULE specifies a certain type
    of symbol. This is not the same as a compilation unit. You can
    have modules which are not compilation units, and compilation
    units which are not modules. How a module is defined varies from
    language to language.