The link role - ARIA Reference Guide

Composites
Represent containers for navigating interactive descendants.
Landmarks
Represent top-level sections of a page, relevant to a specific purpose, that a user may want to scan for quickly and could appear in a site map or table of contents.
Live Regions
Represent dynamic content or announcements, typically updated as a result of an external event when user focus may be elsewhere.
Structures
Represent non-interactive parts of a page that organize content into coherent units.
Widgets
Represent focusable, interactive elements.
Windows
Represent inner windows that are children of the main web document.

WAI-ARIA spec HTML-ARIA spec

Widget(opens in new window)Interactive Content(opens in new window)Phrasing Content(opens in new window)

Description

An interactive reference to an internal or external resource that, when activated, causes the user agent to navigate to that resource.

Allowed Content

Flow content, but with no interactive content descendants, and no descendants with a tabindex attribute specified.

HTML Elements with Implicit ARIA Role

a[href]

Allowed HTML Elements

a[href] (role attribute unnecessary)
button
img
div, span, p, other elements that can receive any role