the.com/thread count

means A measure of how many horizontal and vertical threads are woven into one square inch of fabric, used as a (often overhyped) proxy for how soft or luxurious sheets feel.

from Straightforward textile-industry math, not ancient at all — weavers and mill graders have long counted threads per square inch to grade fabric quality. The term crept out of warehouses and onto bedding packaging as marketers realized a bigger number sells better, which is also why you'll see suspiciously high counts achieved by counting multi-ply threads as several threads each — a loophole that turned an honest manufacturing metric into something closer to bragging rights.