What is the difference between a Claims Made policy and an Occurrence Policy?

A Claims made policy is one where the liability claim must be made during the policy term in order to trigger coverage. An occurrence based liability policy will allow the claim to be filed any time as long as the event that caused the loss occurred during the policy term. Generally the claims made policy is seen as more restrictive coverage and is less desirable from a consumer's stand point. You can read more detail here.