Hosts videos and often embedded across different sites as a default video player.
YouTube is well known as the most popular platform for watching and sharing user-created videos. When a site contains embedded YouTube videos, the videos are still hosted and played by YouTube, meaning it still collects your activity data, even though you are not on YouTube. Google, which owns YouTube, actively collects information about what type of videos you watch and uses that to analyse your behaviour to personalize ads. We know so far that Google collects data about videos you watch and upload, how you interact with them, how long you spend watching a particular video, and any comments that you post on YouTube.
Next to information collected about interactions with YouTube videos, Google is also able to collect information about the specific pages you visited with YouTube-hosted video on it. And it happens without any action on your part since you don't even have to play the video for YouTube to get this data, as the video is loaded in when you load the website .