1. the carrying and storing of food or other items believed necessary for survival, which has been identified as either instinctive behavior, learned behavior, or both. For example, hoarding by rodents varies with the environmental temperature, increasing when the temperature falls and decreasing as the temperature rises. See food caching.

2. a compulsion that involves the persistent collection of useless or trivial items (e.g., old newspapers, garbage, magazines) and an inability to organize or discard these. The accumulation of items (usually in piles) leads to the obstruction of living space, causing distress or impairing function. Any attempt or encouragement by others to discard hoards causes extreme anxiety. It is formally recognized as hoarding disorder in DSM–5, where it is listed in the same diagnostic category as obsessive-compulsive disorder and related disorders. See also cluttering. —hoard vb., n.