Responder has opening values and a fit in the Major suit opening of his partner. The bids and the significance of the bid.
4 shows one of 3 hands.
If opener is interested he bids 4 to ask.
The responses are:
The other other bid available in this system is 4 which informs partner that they have 13-15 points, 4-card trump support and two Aces, and none of the above.
If you and your partner wish to employ this treatment, then it must be noted on your Convention Chart. Your opponents have a right to know the meaning of your bids. Please be so kind as to inform them.