Whats a 4 dimensional coaster

What makes a coaster a four dimensional coaster and why is it called that.

Where the seats spin as the ride is moving. X is the worlds first 4-D coaster.
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Ricochet: Bouncing to you in 2002, Only at King's Dominion!

Thanks

That ride will be a puker IMO ;)
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Got a problem with RWB? you've got a problem with me! Rollercoasters are the secret of life!
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I pray that I will never see a Six Flag Conneaut Lake

And accually, to correct you, it's 4th Dimension, not dimensional. I read it as dimensional in some newspaper, but it's wrong. Check Arrow's website if you don't belive me.
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Hey, SFGAm management, can I buy a couple cages of Sky Whirl?

i never really got why it was called 4th dimension anyways.. that makes all other coasters.. 3 dimensional?

this is why arrow calls it a 4-d: 

When we design rollercoasters we describe the path of the ride using X's, Y's and Z's. To describe the spin or rotation of the riders as they follow the ride path we needed an extra dimension to describe that motion. Hence the 4th Dimension.

Would the 4th dimension be lettered as 'W'? Lol, just goofing off. :)