What is the difference between a one-of-a-kind original art work and a multiple original art work?

Art Work

Some art work is created in the form of a print block. Prints off of the block would all be originals, but there would be multiples of it. Many prints are numbers, 234 of 1000 for example. Another type is when a mold is created and castings are made. Each casting is an original piece of art, but there are multiples of it.

When wood artist create they use a particular type of wood, like oak, for example, and each board used has its own grain pattern even from a different branch of the same tree. So it a wood artist creates an item using oak, and another exact look-a-like in maple, and still another in say mahogany some wood crafter consider the grain and/or wood to constitute a one-of-a-kind. So one of a kind does not always mean that the item is an original.