What Do We Mean by Accessibility, Inclusion & Belonging? — from inclusionhub.com by Jeffrey Howard
Accessibility, also referred to as a11y, is about ensuring systems are designed so everyone can fully participate in public or professional life, while inclusion means everyone has the resources and opportunities they need to realize that. Belonging goes one step further, fostering a culture where everyone feels accepted and supported.

Excerpts:

In this spirit, “a11y” has become a globally recognized rallying cry for greater accessibility—the 11 referring to the software engineering convention of shortening long words to the number of letters they use. A11y has transformed into a symbol for increased accessibility, inclusion, and belonging.

So, if accessibility ensures everybody has the means or tools to reach the table, and inclusion guarantees a seat and relevant opportunities, belonging encourages an emotionally and socially supportive space where each person feels welcome and valued.

It’s easy to tell the difference between when you feel merely tolerated and when you belong.