A Reverse is Not a Convention. With strong hands the rebid can be 2NT (18-19 HCP) or a reverse (17+) or a jump raise (18+) or a jump rebid, a splinter, etc.

N	E	S	W
1§	P	1©	P
3©	. . .			18+ and four Hearts. Invitational to game.
1§	P	1ª	P
2©	. . .			A reverse, showing 17+ points.

Important. This last hand is a vitally important one to understand completely. A reverse is not a convention and cannot be bid with a minimum hand. In the above sequence, opener doesn't have five Hearts and responder doesn't have four, yet opener has bid them at the two level - a strong bid indeed.

A reverse means responder is forced to the three level to take a preference to the first bid suit, and that means opener must have sufficient strength, even opposite a minimum dummy, to make 9 tricks. Don't reverse unintentionally -- plan ahead. Also, plan to reverse when you have the strength. A 2§ rebid after a 1¨ opener sounds really weak - don't have 17+ HCP when you bid this way, even if you must bid a shorter Club suit first.

---

N	E	S	W
1§	P	1©	P
2NT	. . .			18-19 HCP without 4 Hearts or 4 Spades by North. Not forcing, however.
1§	P	1©	P
2ª	. . .			North has four Spades, less than four Hearts, 17+ HCP, yet is unable to open 1NT ? He must need a lot of help in Diamonds for Notrump. 18+ HCP. (1ª is not forcing)
1§	P	1ª	P
3§	. . .			18+ and 6 good Clubs. Invites 3 NT. Not forcing.