An impression counts when your content is exposed to a user. A single user can count for multiple impressions if the user was exposed to the same content multiple times. Impressions do not consider if a user engaged with the content. For example, a YouTube impression is counted when your video’s thumbnail shows up on a viewer’s screen.
An impression is different than reach, but can be considered potential reach. If you have a large amount of impressions, a channel considers that content to be relevant to a large amount of viewers and will present it more often.
Impressions click-through rate represents the percentage of impressions that turned into views. For example, a viewer saw your video’s thumbnail and clicked to watch. It is a good way to gauge brand awareness. Note that if someone accesses your video from a direct link, this will not count in this metric as they were not provided with an impression.
As impressions grow, your click-through rate could lower. There becomes a larger chance the impressions are going to viewers that aren’t part of your target audience… and they may be less compelled to click.
Also, just because someone clicks on your content doesn’t mean they stay engaged. So use click-through rate in conjunction with other metrics to get a more complete picture of your video performance.