Responder's bid.
If the responder holds a 5 card major, he must repeat it !
But there are exceptions, of course :
- With both majors 5th, he jumps and bids the other major (with gathered honors in both majors !)
- With a strong support in one of the opener's suits, and slam ambitions : ... jump raise
♠ Even with a weak hand, repeat your 5 card major