The banner is typically includes things a logo or corporate identity, possibly a site-specific search tool, and is generally what your marketing team would call the header or top banner of the site. If the header element technique is not being used for that banner, a declaration of role="banner" should be used to define a banner landmark to assistive technologies.
Assistive technologies can identify the main header element of a page as the banner if is a descendant of the body element, and not nested within an article, aside, main, nav or section subsection.
Each page may have a banner landmark, but each page should be limited to only one header with the role of banner.
<header role="banner">
<img src="companylogo.svg" alt="my company name" />
<h1>Title</h1>
<h2>Subtitle</h2>
</header>