the.com/sweatpants

means Loose, soft-knit trousers with an elastic waist and no pretensions, designed for sweating, sitting, or giving up on real pants entirely.

from The 'sweat' half is literal — these were born as athletic gear in the early 20th century, worn to make you sweat (or absorb it) during training. 'Sweatshirt' and 'sweatpants' entered the vocabulary alongside the rise of organized gym culture and jogging as exercise, when manufacturers started selling the fleece-lined cousins of wool tracksuits. The irony — that a garment built for exertion became the uniform of maximum non-exertion — is pure cultural drift, not etymology, but it's the twist that gave the word its second life.