Polyester yarn refers to yarn spun from polyester as the raw material. Polyester is a type of fiber made by spinning polymers, often referring to fibers produced using polyethylene terephthalate as the raw material. It is abbreviated as "PET" fiber based on the English name of its raw material, "polyethylene terephthalate." In China, it is commonly known as "滌綸" (dílún). Typically, the term "yarn" actually refers to the general term for both "single yarn" and "plied yarn." In the study of apparel materials, it is defined as follows: "Single yarn" is formed by aligning many short fibers or filaments into an approximately parallel state and twisting them along the axial direction to create a slender object with certain strength and linear density. "Plied yarn," on the other hand, is a strand formed by twisting two or more single yarns together. Yarn is a fine strand made by stretching and twisting fibers such as cotton, wool, hemp, or chemical fibers (often used as raw material for weaving). When multiple fine strands of materials like cotton, hemp, silk, or wool are twisted together, they are referred to as thread.