Plain English Meaning
When something a learner once knew or could do slips away over time and can no longer be recalled or performed reliably.
Full Definition
The loss, partial or complete, of previously learned knowledge or skills, caused by factors such as disuse, interference from new learning, repression of unpleasant material, or weak initial encoding of the information.
Context Anchor
Seen in instructor training when discussing how students retain lessons, review previous material, and maintain flying skills between practice sessions.
Derivation
From Old English 'forgietan' — 'for-' meaning 'away, amiss' and 'gietan' meaning 'to grasp.' The literal sense is 'to lose one's grasp on something,' which fits well: the knowledge was once held, and is now away.