UL = Underwriter’s Laboratory Inc. An independent not-for-profit organisation, set up by the insurance industry for the purpose of establishing product safety standards, that evaluates and certifies the performance and safety of electrical equipment, components and materials.

ultra-fine-pitch As with fine-pitch, a term whose value depends on the date of the definition. The term now (arguably) applies to surface mount packages with a centre-to-centre lead distance of 0.4mm (0.016in) or less.

unsupported hole A hole in a printed board containing no plating or other type of conductive reinforcement.

UUT = Unit under test A term applied to any component or assembly being tested by automatic testing equipment.