Where it appears to the Board of Trade that it would be in the interest of persons for whom any services, accommodation or facilities are provided in the course of any trade or business that any expressions used with respect thereto should be understood as having definite meanings, the Board may by order assign such meanings to those expressions when used as, or as part of, such statements as are mentioned in section 14 of this Act with respect to those services, accommodation or facilities; and where such a meaning is so assigned to an expression it shall be deemed for the purposes of this Act to have that meaning when so used.