What is the difference between an 'occurrence' policy and a 'claims-made' policy in liability insurance?

OCCURRENCE vs CLAIMS-MADE liability policies: OCCURRENCE POLICY: Covers claims arising from incidents that OCCURRED during the policy period — REGARDLESS of when the claim is filed (even years later, after the policy ended); the trigger is when the incident happened; CLAIMS-MADE POLICY: Covers claims that are FIRST MADE (reported) during the policy period; often requires the incident to have occurred after a RETROACTIVE DATE; the trigger is when the claim is made; TAIL COVERAGE (Extended Reporting Period): With claims-made policies, 'tail' coverage can be purchased to cover claims made AFTER the policy ends for incidents during the policy period; RELEVANCE: Common in professional liability, general liability, medical malpractice; the distinction matters for when coverage applies and for continuity when changing policies; occurrence policies provide longer 'reach' for old incidents; claims-made require attention to retroactive dates and tail coverage; understanding occurrence vs claims-made triggers is important casualty/liability exam content.