Indeed, I found that the researcher of CAST (Center for Applied Special Technology) the parallelism their curriculum and UD concept and then they defined the term universal design for learning (UDL) in 1990 (Rose, 2000) that has three principles (Rose, 2001 and CAST, 2008):

Those principles come with some guidelines so that a curriculum can be designed for supporting all individuals with equal opportunities to learn. Thus universal design in the notion of learning means “learning materials, instructions, and activities that make learning objectives can be achievable by individuals with wide differences in their abilities to see, hear, speak, move, read, write, understand English, attend, organize, engage, and remember” (Orkwis & McLane, 1998, p.10). Finally, I understand the UDL and its principles, but one big question is waiting to be answered: How can it be implemented, especially in the online learning? In the next exploration I should find the answer.