The term "rule" shall mean a rule which the Board shall have adopted within the scope of its authority under section 15B of the Act, which shall have become effective in accordance with section 19(b) of the Act or which shall have been amended by the Commission pursuant to section 19(c) of the Act. The term "proposed rule" shall mean a rule of the Board prior to the time when the same shall have become effective in accordance with section 19(b) of the Act.