Hoarding is a compulsive behavior marked by the collecting of primarily useless objects - old newspapers, boxes, bags, knickknacks, etc. Often times, as seen with extreme hoarders, one's home is filled with so many objects he or she barely has a path to walk. Sometimes whole rooms must be sectioned off due to inability to enter. There might even be areas with objects stacked from floor to ceiling.
The cycle begins and ends with anxiety. If you engage in hoarding, you are escaping some anxiety with your compulsive actions. For example, rather than cope with anxiety around boredom, loneliness or loss, you engage in repeatedly collecting and keeping objects to escape discomfort. The more you engage in this cycle, the more your anxiety and compulsive behavior intensifies. The thought of removing any of these objects brings about anxiety and the cycle of collection and avoidance continues.
Click this link for a news story demonstrating some very severe cases involving animal hoarding (note that these cases described more than likely have some mental health concerns in addition to just OCD):
The most effective form of treatment for hoarding is Cognitive-Behavioral Therapy. With motivation and commitment, most who hoard can make great progress.
Follow this link for more information on anxiety disorder treatment