Universal design is design that’s usable by all people, to the greatest extent possible, without the need for specialized design. The term was coined in the 1980s by an architect named Ron Mace, who used a wheelchair due to polio.
“Design that’s usable by all people…”
The challenge of designing for “all people” is including the myriad of individuals and families affected by disability while ensuring that the design is appealing and useful for everyone. Universal design isn’t about disability, but it wouldn’t exist if disability didn’t exist.
“To the greatest extent possible…”
Something that’s universally designed must accommodate as many conditions as possible that affect people’s: vision, hearing, movement, thinking, remembering, learning, mental health, communicating, and/or social relationships throughout all stages of the human lifespan: infancy, childhood, adolescence, early adulthood, middle age, and older age.
“Without the need for specialized design.”
Specialized design is for a specific demographic or need. Universal design is inclusive to any generation someone belongs to or a health condition that someone may have.
Note: yes, some people have significant functional needs that require specialized design. If universal design is the foundation for a design, adding specialized features as-needed is much easier and more cost-effective than if a design is fully specialized.