What does the # in front of a phrase mean?

[Edward]

The # is called a hashtag and means you can follow that topic and read short or send short messages about it in real-time using your computer or cell phone through a program called Twitter. You'll need to sign up to use Twitter on your cell phone or computer. Basically, Twitter is a "network made up of 140-character messages called Tweets. It's a new and easy way to discover the latest news (“what’s happening”) related to subjects you care about." See the link below for more details on twitter and tweets.