In a nutshell, Annotations would allow developers (and Twitter itself, of course) to add additional information to a tweet — such as a string of text, a URL, a location tag or bits of data — without affecting its character count. In other words, such information would be metadata about the tweet or the user who posted it, and would be carried along as an additional payload as it traveled through the Twitter network. Apps and services could then collect that information and filter it or make sense of it.