Can some explain in simple terms what "impressions" are on the internet?

[flowerpot1000000]

So a tweet of mine hit 5,000 impressions, I dont know what this means

Impressions are the amount of times a tweet has been seen.

This includes the times it's been seen in one of your followers timeline and also how often it's appeared in a search OR as a result of someone liking the tweet.

Impressions alone aren't a good measure of the success of a tweet though.It's when it's paired with engagement rate that you get the true (ish) measure of it's success.

The ideal tweet has a high impression number AND a high engagement rate.

Your Engagement Rate is calculated by dividing the number of engagements by the number of impressions. Engagement includes any way someone interacts with a Tweet, including but not limited to, Retweets, clicks and Likes.