After the Stayman rebid of 2 denying a four card major, a rebid by responder of 3 is used to show at least an invitational hand with 5-5 in the majors. Opener rebids:
3 with 3 spades and a minimum hand.
4 with 3 spades and a maximum hand.
Without 3 spades, Opener rebids 3 with a minimum hand.
Without 3 spades, Opener rebids 4 with a maximum hand.
If 1NT opener had 2-2 in majors he bids 3NT. After a 3NT bid by opener, responder can transfer into a major if they want to