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

mangled name
 n.

    A name, appearing in a C++ object file, that is a coded representation of
    the object declaration as it appears in the source. Mangled names are used
    because C++ allows multiple objects to have the same name, as long as they
    are distinguishable in some other way, such as by having different
    parameter types. Thus, the internal name must have that additional
    information embedded in it, using the limited character set allowed by most
    linkers. For instance, one popular compiler encodes the standard library
    function declaration ?memchr(const void*,int,unsigned int)? as ?
    @memchr$qpxviui?.