UDL is a framework to guide the design of learning environments that are accessible and challenging for all. Ultimately, the goal of UDL is to support learners to become “expert learners” who are, each in their own way, purposeful and motivated, resourceful and knowledgeable, and strategic and goal driven. UDL aims to change the design of the environment rather than to change the learner. When environments are intentionally designed to reduce barriers, all learners can engage in rigorous, meaningful learning.
This UDL description is taken from cast.org. CAST is a US nonprofit education research and development organisation that created the Universal Design for Learning framework and UDL Guidelines, now used the world over to make learning more inclusive.