While Twitter has taken over social media, it hasn't yet popped its advertising cherry (and therefore hasn't made money despite its enormous presence on the web). Until now, that is. The social media giant has grown up--it recently announced a plan for advertisers: Twitter Promoted Tweets.
The Twitter Promoted Tweets, much like Google's search ad program for advertisers, allow advertisers to sponsor promotional tweets by purchasing specific search terms. So, when users search for the terms, the advertiser-sponsored tweets will be displayed first. (It took a few years, Twitter, but you did it!)