In social media marketing, engagement is a metric measuring the level of interaction between your audience and your brand. Basically, engagement relates to any action that a user takes on your social media post or social media profile. It generally includes likes, shares, comments, but it can also include mentions, click-throughs, retweets and more. Like for impressions, the way engagement is measured vary from one social media platform to another. Engagement can be seen as an overarching metric for audience interaction, it can be broken down into several metrics (which also vary depending on the platform) such as post engagement, page engagement, engagement rate.
EAT: (Expertise, Authoritativeness, Trustworthiness.)
EAT is a factor of page quality rating for Google, and amongst one of the most important factors. Expertise refers to the content creator. Authoritativeness means having generally recognised authority. People know you, know your background, and look to you as a leader in your industry. They accept you as a good source of information. Finally, Trustworthiness means people can trust you to provide honest, true information that is accurate. The level of EAT required is not the same depending if the content is YMYL or not.