The barrier in bridge is a concept which helps you to describe the strength of your hand to partner. It is used to distinguish between normal (12-15 point) hands and strong hands (16+ points).
Where is it?
If you open 1 of a suit then your barrier for that auction is set at 2 of that suit. So if you open 1♠ then your barrier for that auction is 2♠.
How do we use it?
When you make your first rebid you can show partner an approximate point count by bidding either above or below the barrier.
To show a normal hand with 12-15 points your rebid must be ON OR BELOW your barrier. E.g. if you open 1♣ then you can bid anything up to and including 2♣ and show a normal hand.
If you have 16 or more points then you need to make sure that your rebid is ABOVE the barrier. So if you open 1♣ with 16+ points then your second bid must be 2♦ or above to show your points.
Sometimes you will have a 2 suited hand, but be unable to rebid your second suit without going through the barrier. If you lack the points to bid above the barrier then your only choice is to rebid your opening suit.
Equally, sometimes you will have a hand with 16+ points but only 1 long suit. In this case make sure to jump on the rebid to show your points. If you open 1♠ and have 16+ points then you must rebid 3♠ in order to be through the barrier.
Responder’s Barrier
The barrier is also a concept which can apply to responder. For them the barrier is set with their first response. Bidding above the responder barrier shows game points.
On this hand North opens 1 club. South’s longest suit is diamonds so their first response is 1 diamond. This sets the responder barrier at 2 diamonds.
North has no second suit to show. Rebidding 2 clubs shows a hand with at least 5 clubs and 12-15 points.
South knows that they have game points here. They can show this by bidding 2 spades. 2 spades is above 2 diamonds so it shows game points and a hand with at least 5 diamonds and 4 spades.
On this hand the auction begins the same way. This time though South does not have game points. By the time they get to their second response they must bid above 2 clubs. This means that they cannot show the spade suit without bidding above their responder barrier. They can only repeat the diamonds. With a weak hand themselves North should pass.