Definition of a seed crystal: a small crystal of a substance placed in a solution of the same substance. It acts as a base on which crystals form during crystalization. The crystal which grows will take on the same shape as the seed crystal.

"Dictionary of Science."

Where do seed crystals come from?
I guess they come from molten cooling or solids subliming.

A 'seed crystal' is just an ordinary crystal that you put in your solution. Calling it a seed crystal describes what it's being used for, not some special property of the crystal.

Yes, the seed crystal is just that- a "seed" for a larger crystal network to grow when placed in a super-saturated solution.