Universal Design originally came from architecture. The idea was to design a building that could be used to the greatest extent possible by anyone, regardless of age, ability, etc.
When developing content or materials, it's good to keep Universal Design in mind. Applying Universal Design usually involves including alternative/supplemental formats (like how a stop sign not only uses text but also color) and offering your audience flexibility in choice.
Universal Design for Learning (UDL) is taking the same principles of Universal Design (in architecture) and applying it to Learning.
UDL has three primary components: