Of a <a class="localLink" href="http://schema.org/Person">Person</a>, and less typically of an <a class="localLink" href="http://schema.org/Organization">Organization</a>, to indicate a topic that is known about - suggesting possible expertise but not implying it. We do not distinguish skill levels here, or relate this to educational content, events, objectives or <a class="localLink" href="http://schema.org/JobPosting">JobPosting</a> descriptions.