A conversion is:

When someone reaches your landing page after clicking your ad or video
By definition when someone makes a purchase after clicking on your ad
Any interaction with your ad that can be measured, like watching a video for a certain length of time
An action defined as valuable to your business that someone takes after clicking on your ad

The correct answer is:

An action defined as valuable to your business that someone takes after clicking on your ad

Sources: Google Ads Fundamentals Course

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