Living documentation is documentation that stays true to the system it describes because it is connected to that system and re-examined when the system changes — rather than written once and trusted forever. The defining feature is the feedback loop: a change in the code creates pressure to revisit the corresponding note, instead of letting the two drift apart in silence.
Traditional docs — wikis, READMEs, design pages — are static by default. They capture a snapshot, and from the moment they are saved their accuracy only decays, because nothing links them to the code they describe or signals when that code has moved on. The longer such a page survives untouched, the more of it is quietly wrong, and the more dangerous it is to the next person who trusts it.
Documentation becomes living when each note is anchored to the specific files it governs and flagged for review when those files change. That anchoring is what turns a passive artifact into a maintained one: the system can tell which knowledge a change affects and route it back for a human to keep honest, so the documentation tracks reality instead of aging beside it.