Engagement rate (ER) is a metric that is used to measure the level of engagement that a piece of content or an advertisement receives from its audience. Engagement rate is typically calculated by dividing the number of engagements (such as clicks, likes, comments, or shares) by the number of impressions (the number of times the content or ad was seen by users), and expressing the result as a percentage. Engagement rate is often used to evaluate the performance of an ad or marketing campaign, and to compare the engagement of different pieces of content or ads. A high engagement rate is generally seen as a positive sign, as it indicates that a piece of content or ad is interesting or engaging to its audience.