If you’re using Twitter, then you've definitely seen the use of hashtags. A hashtag is a keyword phrase without spaces that has a pound sign (#) prefix, such as #hashtagsarecool. The main purpose of a hashtag is to allow people to search tweets that have a common topic. You simply click on the hashtagged word and Twitter will pull up all tweets dealing with that word or phrase. And even though they are most commonly found on Twitter, you will also find them on Google+, Instagram and Facebook is now talking about incorporating them into their site.