the.com/mechanical keyboard

means A keyboard built with individual spring-loaded mechanical switches under each key, instead of the cheap rubber dome layer most keyboards use, prized for tactile feel, durability, and often unnecessary loudness.

from 'Mechanical' simply distinguishes these switches — real physical mechanisms of springs and stems, patented in various forms since the mid-20th century — from the rubber dome membranes that took over cheap keyboards in the 1980s for cost reasons. Enthusiasts kept the older mechanical-switch designs (and companies like Cherry kept making them) alive through the membrane era, and the hobby exploded once nerds rediscovered them decades later, so the word didn't change — the rest of the market just got quieter and cheaper around it.