Pattern welding is a special way of constructing

Pattern welding is a special way of constructing a sword blade from a lot of iron / steel parts. Many different kinds of iron / steel parts are fire welded in such a way that a pleasing pattern can be observed on one or both sides of a blade. The pattern results because two sufficiently different kinds of iron / steel that intersect the surface reflect the light differently, in particular after some special polishing or etching.
You thus must use very special shapes of the parts to be welded to produce a specific pattern, and you must use quite different kinds of iron and steel to render the pattern visible. In other words: You must do structural and compositional piling, and you must do it in a way that produces the pattern you are after.
It is time now to look a bit closer at a few words that relate to the ways of making a sword. The first thing to note is that these words and their definitions had not been engraved by the finger of some God in tablets of stone or metal. They have not been handed down as unalterable eternal truth as claimed for some other stuff. There is, for example, no unique and undisputable definition of what "damask" or "damascening" means. It has meant different things to different people at different times. Come to think of it, even in the rare cases where writings in tablets of stone came down from high up, different people at different times interpreted these words differently. They even developed a strong tendency to kill everybody not agreeing with their interpretation even so one of those writings reads rather unambiguously "Thou shalt not kill".
What follows are therefore my personal definitions. I keep as closely as possible to the direct meaning of words, to established meanings in Materials Science, and to customary uses in the iron, steel and swords community. All of these terms I have used and defined before.