Accessibility refers to the extent to which schemas and concepts are at the forefront of people’s minds and are therefore likely to be used when making judgments about the social world.
the ease with which different thoughts and ideas can be brought to mind; an idea that is accessible is already on our minds or can easily be brought to mind
Other /More definition:
Accessibility is the degree to which we can gain access to the available information; the ease with which a schema comes to awareness; how easily something comes to mind
Lexicon of Psychology - Terms, Treatments, Biographies,