Risk pooling is used mostly by insurance providers. It is when a group of people share the cost of the risk especially if the percentage of getting an undesirable outcome is a very high. Risk pooling is done to avoid major losses. For information on what other entities use risk pooling go to this site: http://www.ask.com/wiki/Risk_pool.
The concept of risk pooling is based on the concept of probability. It is used by insurance companies to create a pool that will protect the different companies involved from catastrophic risks like floods, earthquakes and the like.