Glossary

An educational approach with three primary principles:

1. Multiple means of representation, to give diverse learners options for acquiring information and knowledge
2. Multiple means of action and expression, to provide learners options for demonstrating what they know
3.  Multiple means of engagement, to tap into learners interests offer appropriate challenges, and increase motivation

Source: http://www.udlcenter.org/glossaries/glossary_eng#udl

For further reading:
CAST: www.cast.org
UDL National Center: http://www.udlcenter.org