What Does Certificate Of Insurance Mean? 

A document issued by an insurance company/broker that is used to verify the existence of insurance   coverage under specific conditions granted to listed individuals. More specifically, the document lists the effective date of the policy, the type of insurance coverage purchased, and the types and dollar amount of applicable liability.

Investopedia explains Certificate Of Insurance
A certificate of insurance is often demanded in situations where liability and large losses are a concern. For example, a company wishes to hire a driver from a temp agency. The company will most likely ask the agency to show them a certificate of insurance that proves that certain liabilities will be covered by insurance in the event the driver causes problems, such as incurring damages from driving the company’s vehicles.