
Promoted tweets are paid-for messages that appear in search results and on your timeline. Brand owners can now make tweets for specific audiences on Twitter, instead of sending generic tweets to all users.
"Global brands that have different launch dates for several countries can send tailored messages at different times, customised for the users in each country," explains product manager Kevin Well.
If you're an iPhone app developer, you can target your ads to users on that device -- while Twitter fans on desktop and Android will never see the tweet.

The feature is now available to all advertisers, globally, who use promoted tweets. Wells says that sponsored tweets are more likely to appear if they are clicked on, so "advertisers are rewarded for messages that resonate with audiences".
A recent report in the Wall Street Journal said that Twitter generates the majority of its revenue from adverts shown on mobile devices. On advertiser said the "results were staggering" -- a million people interacted with its advert, with roughly 70 percent of those clicks being from a phone or tablet.
Source : Wired