ULEF stands for Ultra Low Emitting Formaldehyde. To qualify, a product must come in at or under 0.04 ppm. (As a reminder, regular CARB plywood levels are 0.05 ppm.)
ULEF is an emissions standard, not a content condition (emitting, right?) (see my blog on emissions vs. content standards)—so any type of formaldehyde glue might be acceptable. Many Melamine Urea Formaldehyde (MUF) resins can meet the ULEF standard. In fact, in some of the older LEED credit categories, where they still asked for “NAUF” (No Added Urea Formaldehyde), they have been amended to say "NAUF or MUF if CARB-certified as ULEF." (Of course, as previously discussed, later LEED has dropped the content focus on formaldehyde entirely and gone for emission-based evaluations.) So while ULEF remains a condition to look for in green building, on a practical basis the biggest benefit is that manufacturers that qualify for ULEF production can have reduced testing requirements under CARB.