def is_word(pos_tag):
    """Return ``True`` if ``pos_tag`` is not punctuation, False otherwise.

    This method checks that the ``pos_tag`` does not belong to the following
    set: ``{'PUNCT', 'SYM', 'SPACE'}``.

    :param pos_tag: Part of Speech tag
    :type pos_tag: string
    :return: True if POS is a word
    :rtype: boolean
    """
    return pos_tag != 'PUNCT' and pos_tag != 'SYM' and pos_tag != 'SPACE'
