What Is a Banner?

In online marketing the word has two meanings. The first and older one is the banner ad: an image or animation of fixed size that appears on a page and leads to the advertiser's website. It is the basic form of display advertising.

The second meaning is broader: any strip a website places above, below or within its content to highlight something of its own. A cookie notice, a free-shipping message, an invitation to download an app or a reminder about an offer are all banners in this sense, even though they do not sell space to third parties.

Banner ad sizes were standardised for years in fixed pixel dimensions. The IAB, the digital advertising industry body, now recommends in its New Ad Portfolio, last updated on 25 February 2025, flexible formats that adapt to different screen sizes and devices, while acknowledging that many companies still produce fixed-size formats.

A banner ad is almost always served by an ad platform. The page reserves a slot, a script requests an ad from the platform, the platform decides which one to show based on the auction and targeting, and the banner loads into that slot. The advertiser pays per impression or per click, and the platform counts both.

A site's own banners, such as a cookie notice or a promotion, are usually inserted with JavaScript once the page has loaded. That has two technical consequences. First, if the banner appears late and pushes the content down, the page jumps, which Google measures as CLS within the Core Web Vitals. Second, a banner that only exists after JavaScript runs is not in the HTML read by a crawler that does not run that code.

Over time, people learn to ignore whatever looks like advertising. Nielsen Norman Group calls this banner blindness: in its eyetracking study published in April 2018, participants' eyes avoided elements with the look or position of an ad, even when they contained useful information.

For SEO, the key point is how much the banner covers. In its guide to interstitials and dialogs, Google recommends using banners that take up only a small fraction of the screen instead of interstitials that cover the whole page, so users and search engines can reach the content as soon as they land. It also advises against redirecting to another page to collect consent: if every URL redirects to a single page, Googlebot can only crawl that one.

For user experience, banner blindness has an awkward implication: an important message that looks like an ad can go unnoticed. A free-shipping notice designed like a banner ad risks being read by no one.

On zds.es we handle it like this, checked in the source code on 8 October 2026: the cookie notice is not in the HTML the server delivers. There is an empty container that a consent library fills in the browser, and until the visitor decides, the Google Analytics configuration starts with every storage and advertising permission set to denied (Consent Mode v2). For a crawler that does not run JavaScript, the notice does not exist, and the content is visible from the first line of the HTML.

• Design your own notices as strips that take up a small part of the screen, not as layers over the whole page.
• Reserve the banner's space in the layout so its appearance does not push the content.
• Do not redirect to a separate page to ask for cookie consent.
• Visually separate important information of your own from the look of an ad, so it does not fall victim to banner blindness.
• Check on mobile how much each banner takes up, because a reasonable strip on desktop can cover half the screen there.
• If you sell ad space, offer flexible formats that adapt to screen size, as the IAB recommends.

• Showing an interstitial on arrival that covers all the content to promote something of your own.
• Inserting banners without reserved space, so the page jumps while people read.
• Stacking a cookie notice, a promotion and an app prompt at the same time until the content is barely visible.
• Giving an important message, such as a price change, the look of an ad.
• Measuring only clicks on a banner without checking how much it bothers people who came to read.