[CDWasten]

What does 3 no trump mean in response to your partner's opening 1 in a major. There are no intervening bids. I have 12 HC points KJx in spades

Thank you.

[Vampyr]

A popular treatment in England is the "pudding raise", a minimum-GF flat hand with enough trumps to add up to eight with whatever you promise.

I play it as a raise with a void over 1♠, and a spade splinter over 1♥ with 3♠ being the raise with void to save space.

Then of course, there is "to play".

[Stephen Tu]

No std meaning, avoid using it without prior discussion. There are a ton of different options, some natural and an offer to play, others raises of various types.

I've seen played at least:
16-17 balanced

4333 raise 3cd support choice of games

4 cd balanced raise, forcing, various ranges

Splinter raise to distinguish either range or singleton vs void

Preemptive weak raise to 4M, but with say a side ace, giving partner with a moose a better estimate of slam chances.

[Cyberyeti]

We play it as a 4333 with a 4 card minor 13-15 so that opener can try to make a sensible choice with 5 cards in his major. If you play a forcing NT and have other ways to bid that hand, you may not need it for that.

[ahydra]

Should be 4333 (4 in opener's suit if playing 4-card majors, 3 (with the 4 not in the other major) if playing 5-card majors), scattered values to make 3NT from your side attractive, and about 13-16 HCP or so.

ahydra

[alok c]

If you have not discussed earlier with partner the specifics then it is a gamble & Primarily to play. If you are playing 5c majors then 3nt bidder is expected to hold at most 3c in bid suit preferably with a top honours(hoping to run 5 tricks & score 4 tricks elsewhere) with 12/13 points with no biddable suits & scattered values with at least 3cs in unbid suits.

[Vampyr]

You should also be thinking about a 3NT response to 1m. If your agreement is "to play", I can practically guarantee that you will miss a slam every time it comes up.

[NickRW]

Absent discussion, I would think it is "to play", but as others have said, it has various possible meanings. Sufficiently many and sufficiently often used that I wouldn't put my partner in a quandary absent that discussion.