I believe PT300 hit it right on the head. A coaster that cannot be classified as one of the two main classic designs, an out and back, or a twister (I don't know if a terrain coaster is a classic design also), is simply known as and classified as a freeform. A steel freeform is just a, well, steel freeform coaster. I'm sure that there can be a wooden freeform too.
Steel Freeform...kinda sounds futuristic to me...:)
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"Shut up brain, or I'll stab you with a Q-tip!"
~From the brilliant mind of Homer J. Simpson.