UL stands for Underwriters Laboratories, an organization that has been around for more than 100 years. If you visit the UL Web site at www.ul.com, you can find the following description:
"UL is a world leader in product safety testing and certification. For more than 100 years, manufacturers have had their merchandise evaluated and tested for safety risks by our independent, third-party safety certification organization. Last year alone, approximately 14 billion products with the UL Mark entered the global marketplace."
A good nine-word summary used by UL is, "A not-for-profit organization dedicated to public safety."
UL sets standards for different product categories and tests products to make sure they meet the standards. In this way, UL is similar to the CE marking organization. UL may also certify the installation of products in the field.
Underwriters, by the way, are insurers. According to Encyclopedia Britannica, "The word underwriter is said to have derived from the practice of having each risk taker write his name under the total amount of risk that he was willing to accept at a specified premium."
To learn more, see the links below.