5S is a workplace organization method built on five Japanese-origin steps — Sort (seiri), Set in Order (seiton), Shine (seiso), Standardize (seiketsu), and Sustain (shitsuke). The goal is a workplace where everything has a place, abnormalities are obvious at a glance, and waste from searching, waiting, and motion disappears.
It is the foundation of nearly every lean program because it makes problems visible and creates the discipline that sustains every other improvement. Without 5S, more advanced techniques like standard work and poka-yoke rarely hold.