in social media, such as Twitter, using a hashtag (#) allows other users to view all messages using the word that follows. If you're a Detroit Lions fan, you could send a message like this "looking forward to tomorrow's game #detroitlions". By also typing #detroitlions, both the other Lions fans in the world could see your message - and any other messages posted using that same hashtag.

I would assume that someone named Cassidie created his or her own hashtag so friends and relatives could track all affected messages