Twitter is s social networking service that lets the users send and view 140 characters or less messages that are known as "tweets." It was created in March 2006 by Jack Dorsey, Evan Williams, Biz Stone and Noah Glass and was offically launched in July of the same year. It has gained a lot of popularity and as of May 2015, Twitter has had over 500 million users.
What can always be seen on twitter is a hashtag. A hashtag (#) is a type of label used on twitter to categorize tweets by what is used in the hashtag. People use it for sporting events, news, award shows, politics, almost anything.
Users on Twitter also use hashtags to search for tweets in order to be informed about a certain topic that is happening. There are always "Trending Topics" going on in Twitter and hashtags let people see what is going on in those topics.
Hashtags have helped events and topics be known to the world so that the public can be informed about what goes on.