A conversion is:
By definition when someone makes a purchase after clicking on your ad
When someone reaches your landing page after clicking your ad or video
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
Explanation:
An action that’s counted when someone interacts with your ad (for example, clicks a text ad or views a video ad) and then takes an action that you’ve defined as valuable to your business, such as an online purchase or a call to your business from a mobile phone.
Read more here: https://support.google.com/partners/answer/6365
