Definition
Knowledge loss is the permanent disappearance of an organization's working context: the moment the reasoning behind a decision, the history of a relationship or the cause of a process exception exists only in one person's memory or one retired system, and then becomes unreachable. Its defining property is that it is silent. Nothing fails at the moment of loss; the cost appears later, when the organization tries to reconstruct why.
Why it matters
Every organization treats knowledge loss as a human resources problem and manages it with handovers, documentation drives and exit interviews. All three fail for the same reason: they ask people to write down, in their last two weeks, context they accumulated over years and no longer notice they hold. Knowledge loss is an architecture problem. If memory is captured continuously as work happens, there is nothing to hand over, because nothing was ever only in someone's head.
Where it comes from
Studied in knowledge management under headings such as knowledge attrition and expertise loss. The Human Layer series reframes it as a consequence of missing infrastructure: organizations do not lose knowledge because people leave, they lose it because memory was never held anywhere but in people.
Read the source papers: The Human Layer · The Sovereign Memory Layer