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The Resource Center / Viewability

Viewability Glossary

There are many terms that are used in discussions about viewability. This glossary was gathered from recognized industry sources including the MRC, IAB and comScore (visit their site for additional terminology and definitions).


Above the fold [ATF]

Ads which appear in digital environments in a location on the screen that can be immediately viewable upon opening the browser. Ads which run further down the page and require the consumer to scroll down to see the ad are not considered ATF but rather below the fold [BTF].



How well an ad achieves a marketing objective such as increasing sales of a product in a store or lifting the brand perception of a company. Viewable impressions are not measures of effectiveness but rather minimum standards of ad delivery.

Engagement / Attention Metrics

Ad delivery metrics which demonstrate the consumer of the ad has gone beyond the minimum viewable impressions standard. Examples of engagement metrics include the duration a consumer has spent with a video ad playing or direct mouse interactions with a display ad.



As a platform for digital advertising, “desktop” often refers to both laptop and desktop computer devices.


Fraudulent traffic

Traffic to a website that is generated intentionally to extract money from the digital advertising ecosystem without the presence of a legitimate audience.



Gross Rating Point. A measure of transaction typically used in TV but increasingly used in digital. A GRP is a measure of a number of impressions as determined by the reach times frequency of those impressions. In digital, in order for a GRP to be comparable with a TV GRP, the impressions used in the GRP calculation must be viewable impressions. Often in digital this is referred to as a vGRP.



As it relates to mobile advertising, “in-app” refers to an environment in which ads may be delivered to a consumer through an application (app) on the mobile device. This is in contrast to the “in-browser” environment. Types of in-app environments include in-app native, in-app embedded browsers and in-app embedded ad frames.


As it relates to mobile advertising, “in-browser” refers to an environment in which ads may be delivered to a consumer through their mobile browser (such as Safari or Chrome). This is in contrast to the “in-app” environment.


A technique to place an ad in a different invisible frame than the rest of the content on the page. To the consumer of the page the ad appears as if it’s on the page but it’s actually located on a different page and just seen through the iframe opening. When ads and content are on different pages because of iframes, measuring actual viewability can be more complex.

Invalid traffic [IVT]

Traffic to a website that is generated, either intentionally or unintentionally, by invalid sources. This includes non-human and fraudulent traffic, as well as other sources of online traffic that is not generated by natural consumer browsing behavior. All traffic which is IVT is automatically determined to not count as a viewable impression. Because identification of IVT varies vendor to vendor, differing amounts are removed from viewable impression calculations by different measurement vendors, causing discrepancies. IVT is also referred to as non-human traffic [NHT].


Making Measurement Make Sense [3MS]

A cross-industry initiative founded by the American Association of Advertising Agencies [4A’s], the Association of National Advertisers [ANA], and the Interactive Advertising Bureau [IAB]. The Media Rating Council [MRC], an independent body, is responsible for setting and implementing measurement standards. The 3MS mission is to define, across the marketing ecosystem, clear standards-based metrics for interactive advertising that are comparable to traditional media.

Measurability rate

This refers to the rate at which a given vendor can measure ads for viewability. Because technology varies by vendor, measurability rates will also vary from vendor to vendor.

Measurable impressions

In digital advertising, not all ads that are served can actually be measured for viewability. This is because some ad delivery environments – such as cross-domain iframes within mobile browsers – can prevent today’s measurement technology from accessing the information needed for viewability analysis. “Measurable impressions” refers to the number of impressions for which viewability measurement was possible for a given measurement vendor.

Measurement tag

A piece of code appended to the advertising creative that sends data to the measurement provider when the ad loads in the browser so viewability can be determined.

Media Rating Council [MRC]

An independent industry organization that aims to secure valid, reliable and effective measurement services for the media industry. The MRC has established criteria for viewable impression reporting, and administers an audit and accreditation system to inform users as to whether measurement services meet the established criteria.


As a platform for digital advertising, “mobile” often refers to both smartphone and tablet devices.


Non-human traffic [NHT]

Another term for invalid traffic [IVT].



In digital ad delivery, “optimization” refers to the process of revising the ad delivery strategy to improve performance against campaign goals. Ad optimization is often done during the flight of a campaign.

Opportunity to be seen [OTS]

This means the ad was placed in a manner that could be seen by a consumer but does not mean the consumer actually saw it. When ads run in digital and they never even appear on the consumers screen because they are too far down the page, they have no OTS.



In advertising, the location on an advertising platform where an ad will be placed. Because viewability relies on the ad loading on the screen, different ad placements will have differing viewability rates based on user activity. For example an ad may run on the top of a page in an above the fold placement, while a different ad runs along the side of the page in a different placement and a third runs at the bottom of the page in yet another placement.


In digital advertising, “platform” refers to the medium in which the ad is served. This can include mobile and desktop, display and video, in-browser and in-app, as well as other media for advertising.


Occurring before the advertising media purchase takes place. In some programmatic environments, ad buying resembles an auction in which potential buyers place “bids” on desirable advertising inventory. An advertiser may want to understand the likelihood that inventory will meet certain criteria (such as viewability) before bidding on it – that is, pre-bid. Pre-bid viewability is a best estimate that an ad will be viewable but does not guarantee it.


Robots, Bots, Bot Nets, Spiders, Crawlers

Various terms which represent automated, non-human computer programs that can consume impressions and appear to generate ad reach. They are considered invalid traffic and should be removed from counts of viewable impressions.


Tag rotation

When there are multiple creative assets that need to be shown in a given ad placement, the tags can be rotated by an ad server. When evaluating the effectiveness of viewable impression measurement vendors, the built-in tag rotation capabilities of the ad server can be used to rotate identical creative assets, all carrying a unique measurement vendor tag in equal rotation. This ensures the measurement vendor tags do not impact each other and eliminates the need for sites to develop their own custom tag rotation code.



The opportunity of an ad to be seen by a consumer. In order for a digital ad to be viewable, a portion of the ad must render on a consumer’s screen for a given amount of time. In the US, the MRC has recommended specific minimum requirements for viewability for ads delivered in display, video and mobile environments based on these terms. If an ad is viewable it does not mean the ad was viewed, was engaging or that it captured attention.

Viewable impressions

In digital advertising, not all ads that are served have the opportunity to be seen by a viewer. The term “viewable impressions” refers to the number of impressions that meet the criteria for viewability. This is equivalent to ads running on traditional platforms such as TV where ads have an opportunity to be seen. Viewable impressions are a minimum condition for trading, not a measure of success. IVT may never be considered a viewable impression, even if the robot or spider generating the traffic appears to meet the viewable impression definition.

Viewed impressions

Impressions that appeared and on a screen AND were definitively seen by a consumer. Custom studies using techniques such as eye tracking or neutral response can measure this but it is not widespread or easily traded on.


validated GRP. A GRP where all impressions included in the GRP calculation are viewable impressions, free from invalid traffic, not blocked for brand safety issues and in the correct geographic country. This is comparable to a GRP on television.