A Short Definition of Compulsive Hoarding (Article taken from Wikipedia) by Miguel Medina

Compulsive hoarding
Compulsive hoarding (or pathological hoarding or disposophobia)^[1] is the excessive acquisition of possessions (and failure to use or discard them), even if the items are worthless, hazardous, or unsanitary. Compulsive hoarding impairs mobility and interferes with basic activities, including cooking, cleaning, showering, and sleeping.
It is not clear whether compulsive hoarding is an isolated disorder, or rather a symptom of another condition, such as obsessive-compulsive disorder.^[2]

Characteristics

While there is no clear definition of compulsive hoarding in accepted diagnostic criteria (such as the current DSM), Frost and Hartl (1996) provide the following defining features:^[3]

• The acquisition of and failure to discard a large number of possessions that appear to be useless or of limited value
• Living spaces sufficiently cluttered so as to preclude activities for which those spaces were designed
• Significant distress or impairment in functioning caused by the hoarding
• Reluctance or inability to return borrowed items; as boundaries blur, impulsive acquisitiveness could sometimes lead to kleptomania or stealing

According to Sanjaya Saxena, MD, director of the Obsessive-Compulsive Disorders Program at the University of California, San Diego, compulsive hoarding in its worst forms can cause fires, unclean conditions (e.g. rat and roach infestations),^[4] injuries from tripping on clutter and other health and safety hazards.^[5]
The hoarder may mistakenly believe that the hoarded items are very valuable, or the hoarder may know that the accumulated items are useless, or may attach a strong personal value to items which they recognize would have little or no value to others. A hoarder of the first kind may show off a cutlery set claiming it to be made of silver and mother-of-pearl, disregarding the fact that the packaging clearly states the cutlery is made of steel and plastic.
A hoarder of the second type may have a refrigerator filled with uneaten food items months past their expiration dates, but in some cases would vehemently resist any attempts from relatives to dispose of the unusable food. In other cases the hoarder will recognize the need to clean the refrigerator, but due (in part) to feelings that doing so would be an exercise in futility, and overwhelmed by the similar condition of the rest of their living space, fails to do so.