Hashtag campaigns have emerged as one of the most powerful social media techniques for quickly initiating conversation on a particular issue.
By using the # (hashtag) symbol in front of a word or group of words with no spaces between them, Twitter categorises any tweets that make use of the exact same hashtag. This means that anyone searching for a particular hashtag gets a listing of all tweets that contain this hashtag organised by date. Here are examples of two such campaigns.
#shoutingback