What does the term "viewability" mean in the context of online advertising?

In the context of online advertising, "viewability" refers to whether an ad had the chance to be seen by a user. This metric is crucial as it focuses on whether the ad was actually in a position on the webpage that a user could potentially view it, rather than merely counting impressions where the ad may not have been visible on the screen.

Viewability is typically measured against standards set by organizations like the Interactive Advertising Bureau (IAB), which defines an ad as viewable if at least 50% of the ad's pixels are in view on the screen for a minimum of one second for display ads, and two seconds for video ads. Understanding viewability helps advertisers and publishers assess the effectiveness of their ad placements and can influence their bidding strategies and overall media buying decisions.

The other options, while related to advertising metrics, do not correctly encapsulate the specific meaning of viewability. The total number of impressions refers to how many times an ad has been displayed, regardless of whether it was seen. The duration of time an ad is on a webpage does not guarantee that it was seen, and the percentage of an ad viewed compared to its total size doesn't align with the standard industry definitions and measurements of viewability.