Source : WordNet®

binary file
     n : (computer science) a computer file containing
         machine-readable information that must be read by an
         application; characters use all 8 bits of each byte

Source : Free On-Line Dictionary of Computing

binary file
     
         A file containing {binary} data,
        i.e.  arbitrary bytes or words, as opposed to a {text file}
        containing only printable characters (e.g. {ASCII} characters
        with codes 10, 13, and 32-126).
     
        On modern {operating systems} a text file is simply a binary
        file that happens to contain only printable characters, but
        some older systems distinguish the two file types, requiring
        programs to handle them differently.
     
        A common class of binary files is programs in {machine
        language} ("{executable} files") ready to load into memory and
        execute.  Binary files may also be used to store data output
        by a program, and intended to be read by that or another
        program but not by humans.  Binary files are more efficient
        for this purpose because the data (e.g. numerical data) does
        not need to be converted between the binary form used by the
        {CPU} and a printable (ASCII) representation.  The
        disadvantage is that it is usually necessary to write special
        purpose programs to manipulate such files since most general
        purpose utilities operate on text files.  There is also a
        problem sharing binary numerical data between processors with
        different {endian}ness.
     
        Some communications {protocols} handle only text files,
        e.g. most {electronic mail} systems before {MIME} became
        widespread in about 1995.  The {FTP} utility must be put into
        "binary" mode in order to copy a binary file since in its
        default "ascii" mode translates between the different text
        line terminator characters used on the sending and receiving
        computers.
     
        Confusingly, some files produced by {wordprocessors}, and
        {rich text} files, are actually binary files because they
        contain non-printable characters and require special programs
        to view, edit, and print them.
     
        (2002-01-19)