Kokish relay (invented by Canadian star, Eric Kokish) is used by a 2 opening bidder.
In this system, after 2-2 (waiting), opener has several ways to show strong balanced hands.
2-2-2NT shows 22-23/24 (more than a 2NT 20-21 opener).
2-2-2 is artificial and requests that the responder bids 2 after which:
2NT=24/25+ Balanced and forcing
The ranges shown are approximate. The point is that with a huge balanced hand worthy of game, opener doesn’t have to eat up space by jumping to 3NT. He can Puppet to 2 (via 2) and then bid 2NT which is now forcing (responder must bid even with 0 points). Responder can use Stayman and Transfers on the 3-level.
What does opener do with an actual heart suit? He bids 2 and then after the 2 Puppet, he bids something other than 2NT. If he repeats the hearts it shows a 6+ card suit. If he bids a new suit, it shows that suit and hearts. So, for example, 2-2-2-2-3 shows 5+ hearts and 4+ clubs (forcing)–it «cancels the message of the Kokish relay.»
Using this system, 2-2-3NT can be used to show a «trick-taking» hand such as:
K 2 K 8 2 A Q A K Q 8 7 6.
The 2 bid (and subsequent 2 Puppet) are alertable.