Accessibility refers to the design of products, devices, services, or environments for people who experience disabilities. The concept of accessible design and practice of accessible development ensures both "direct access" (i.e. unassisted) and "indirect access" meaning compatibility with a person's assistive technology (for example, computer screen readers).
Accessibility can be viewed as the "ability to access" and benefit from some system or entity. The concept focuses on enabling access for people with disabilities, or special needs, or enabling access through the use of assistive technology; however, research and development in accessibility brings benefits to everyone. -- https://en.wikipedia.org/wiki/Accessibility
This guide will provide you with information about creating accessible digital materials.
Accessibility in the Laboratory by 
Accessible Instructional Design by
The Advances in Special Education Technology series is designed to focus international attention on applications of technology for individuals with disabilities. Outstanding researchers from around the world will contribute chapters synthesizing the research evidence on specific types of technology applications that improve access, engagement, and learning outcomes of diverse learners. The scope of contributions will cover subfields known as assistive technology, instructional design, instructional technology, online learning, personalized learning, and universal design for learning and will encompass both formal and informal learning settings across the lifespan. Instructional designers often fail to consider issues of accessibility when creating educational materials. As a result, students with disabilities frequently encounter physical, sensory, or cognitive barriers that prevent them from accessing, engaging, and succeeding in learning activities. This volume will examine issues of accessibility and how designers can improve the quality of educational materials by embedding supports that anticipate the special learning needs of diverse learners.
Modular Online Learning Design by 
Teaching to Diversity: The Three-Block Model of Universal Design for Learning by
In her book Teaching to Diversity, Dr. Jennifer Katz synthesizes the research, and 16 years experience of teaching in inclusive classrooms and schools, to provide answers to several questions: How do I make inclusion work for ALL students? What are the foundational best practices of a truly inclusive learning community? How does one create such a community? The author pulls together, in an organized way, a three-block model of universal design for learning (UDL) and suggests a step-by-step approach for implementing it. This framework includes: Block One, Social and Emotional Learning: details ways to build compassionate learning communities (K-12) in which all students feel safe and valued, and develop a positive self-concept, sense of belonging, and respect for diverse others. Block Two, Inclusive Instructional Practice: includes a framework for planning units from K-12, and explains instructional and management practices for teaching, assessing, grading, and reporting in UDL Classrooms. Block Three, Systems and Structures: suggests strategies for creating inclusive learning communities, and explores ways in which resource teachers, student services personnel, and school administrators can support and create socially and academically inclusive schools and classrooms. The three-block model of UDL can empower educators with the knowledge, skills, and confidence required to teach diverse learners in the same classroom--including those who have previously been excluded. Ultimately, it is about creating classrooms and schools that heal by teaching to the heart, mind, and spirit of every student.
