Top influencers are users who have the most impact in terms of reach. Their tweets are retweeted by a number of followers. For instance, if an influencer posts a tweet which is retweeted by 5 followers, then their reach extends to their followers as well as the followers of the 5 users who retweeted, combined.
To further illustrate this, let’s assume that the influencer himself has 10,000 followers and the 5 followers who retweeted have 1,000 followers each. This means that the total reach of your tweet is 10,000 + (5 x 1,000), i.e. 15,000 people.
Active users are the ones who make the greatest contribution in terms of Tweets and Retweets as well as replies. To put it simply, the user who has the highest count of tweets, retweets and replies is the most active user.