The Red Suit Transfers we know all about. 2D & 2H are transfers to the suit above after a 1NT opening. So what does 2S mean?
Partner opens 1NT and it’s passed to you. 1NT doesn’t look like a good contract, does it. Big hole in hearts, which, if you pass, may well be filled by your left hand opponent bidding the suit. So you need to do something. But what? You can’t bid 2D as that’s a transfer to hearts. 3D is a mild slam invitation in that suit, which you certainly don’t have, so you’re a bit stuck … unless we can use 2S as a “minor suit transfer.”
The bidding goes:
1NT - PASS - 2S - PASS
Now partner must “complete” the transfer and bid 3C. With the given hand you have other plans, so it continues:
3C - PASS - 3D.
Obviously, had your suit been clubs you would have passed. This a weak manoeuvre, designed to be obstructive and/or guide partner to the best place to play the part-score.
Let’s just summarise that:
A 2S repsonse to a 1NT opening bid forces opener to bid 3C. The 2S bidder passes with a 6-card club suit, or “corrects” with a 6-card diamond suit.
Don’t use this manoeuvre with a 5-card only minor suit, just pass 1NT.