Banner is an area below header. It’s optional to use. You can set common banner for the whole site, different for each category or page type, or even make it unique for each page or post. One of the following content types can be used as a banner:

• Layer slider
• Classic slider
• Image
• Empty space (of any height)
• Custom content

In that case an image is used as a banner

Read more also about sliders, or watch a few examples of another banner use: