Serious 3NT is a contract bridge bidding convention. It is used in game-forcing auctions where a major suit has been agreed upon.
1♠–2♣ if using 2/1 Game Forcing or 2♠–3♠ (Agreeing spades)
The next bid indicates suitability for slam:
Since Spades are the agreed trump suit, Three No Trump is not usually the best contract. Using Serious Three No Trump, a bid of Three No Trump says "I am Serious about slam", i.e. "I have a good hand". Bypassing bidding Three No Trump says "I am not Serious about Slam". Examples shown in the above auction.
If one player bypasses 3NT with a Cuebid (and is 'not serious'), then a Cuebid by partner indicates that he is serious. Note that in the example auction above, if the strong hand is next (after the 3♠ bid, he can differentiate between a strong hand, a weak hand that has a control (in case partner is strong) or a minimum hand.
Serious Three No Trump was devised by and named by Eric Rodwell.
Zorro lies dying
In the Spanish sun
All the women crying
Especially the pretty ones
He drew his sword...
They came with guns
Stealing is stealing
I've done lots of that
Now reach into my pocket, padre
Hide this gold pouch in your hat
And let the skinny peons
Feed upon the fat
It was liberated
From some aristocrat,eh?
So pray for him father
You need not bother
Cause I am the fox
And I go where I want
If heaven ignores me
The devil adores me
Yes, I am the fox
And I go where I want
Padre, don't it seem
Hundred years ago
Before I donned the mask
I'm Don Diego
Now there's only minutes left
For the cunning El Zorro
Go fetch my sword, my horse
I'll ride out death Diablo
So pray for him father
You need not bother
Cause I am the fox
And I go where I want
If heaven ignores me
The devil adores me
I am the fox
And I go where I want
Death you're running closer
And I can't keep this pace
Sir, I'm disadvantaged
And should I lose this race
Hand to me your deadliest wine
I'll give you back a taste
Before you burn your mark on me
I'll carve mine in your face
So pray for him, father
You need not bother
Cause I am the fox
And I go where I want
When Satan annoys me
Then heaven employs me
Cause I am the fox
And I go where I want to go