Banner advertising consists of placing a graphical banner advertisement (typically, a 468×60 pixels) on a web page.
Display ads are advertisements you view from a web browser (on a computer or mobile device).
They are the ads you see while browsing.
They can be banner ads shown on the top of the page or skyscrapers running up the sides.
It's an ad format
The role is to catch the eye of incoming traffic to the page, enticing readers to click the advertisement.
See Ad - Size
This form of monetization is implemented by both
UI - Visitor Eye (Visitor's attention / Visual Order)