the tendency of web visitors to ignore banner ads, even when the banner ads contain information visitors are actively looking for.

This term describes the phenomena that people have become desensitized to banners and simply pass over them without clicking. Some ways to overcome banner blindness are to place banners in less typical areas of a page (like in the middle of content) or to use banner sizes that are different from the standard 468 x 60 pixels.

in earlier days of the internet, banners and banner advertising became so ubiquitous that people started becoming desensitized and "immune" to them, and as a result usually ignore them instead of clicking them, hence the term banner blindness. Positioning the banners in places web searchers typically didn't expect them is a possible remedy to this.