Facebook Announces Hashtags
First mentioned in March, the rumors are now confirmed with Facebook announcing that users are now able to create and click on hashtags. Similar to other services such as Twitter, Instagram and Tumblr, users can now search for hashtags and share their posts or pages.
A hashtag is a word that has a hash symbol (#) in front of it and allows users to join a discussion as well as search for the hashtag. While other social network services such as Twitter have this feature, the difference is that Facebook allows users to decide on their audience every time they make a post so posts can either be read by the public or a select audience.
Source: Facebook Newsroom