HTML5 defines structural elements, called regions, for header, nav, main, footer, and aside elements in a web page. ARIA provides landmark roles for these same things. Either provides navigation to significant page areas. Some applications may contain important areas that do not fit into one of these defined regions or landmarks. In this case, you can define a custom or generic region using ARIA’s role=”region”. Each region must be given a descriptive label via aria-label or aria-labelledby. When defined, these generic regions can be navigated along with other regions/landmarks.
See also information about how you can subscribe to the monthly WebAIM Newsletter which contains lots of great information about web accessibility.