Accessibility means designing products, devices, services, vehicles, or environments so that they’re accessible to specially-abled people. A big part of the concept is to enable people with disabilities through assistive technologies (screen readers, keyboard detection, and other assistive technology).
To create accessible things means to create something that is accessible to all (whether they have a disability or not). Users can use an application to achieve established goals with effectiveness, efficiency, and convenience and not be confused with accessibility, which is how users can use an application in a specified context.