Similar to other services like Instagram, Twitter, Tumblr, or Pinterest, hashtags on Facebook allow you to add context to a post or indicate that it is part of a larger discussion. When you click on a hashtag in Facebook, you'll see a feed of what other people and Pages are saying about that event or topic.
The hashtags can also be used informally to express context around a given message, with no intent to actually categorize the message for later searching, sharing, or other reasons. This can help express humor, excitement, sadness or other contextual cues, for example, "Just found out my dad is my Chemistry teacher. #awkward" or "Thank God, it's Friday!! #excited"
According to Facebook, now you can:
• Search for a specific hashtag from your search bar. For example, #BBATheChase.
• Click on hashtags that originate on other services, such as Instagram.
• Compose posts directly from the hashtag feed and search results.
For instance, if you add #BBATheChase at the end of your status update, your friends that search for #BBATheChase, just to follow conversations about Big Brother Africa (The Chase) will see your update and probably join the conversation.
If you search for #BBATheChase using the search bar on Facebook, you'll get a list of updates related to the TV show, thereby making it easier for you to discover what others are saying about the Big Brother Reality TV show and participate in the BBATheChase public conversations. What you won't get are updates that say "I am watching BBATheChase" because "BBATheChase" isn't preceded by the hash tag (#).
Remember, any combination of characters led by a pound sign (#) is a hashtag, and any hashtag, if promoted by enough Facebook users, can "trend" and attract more individual users to join conversations using the hashtag.
Facebook promises to continue to roll out more features in the coming weeks and months, including trending hashtags and deeper insights, that help people discover more of the world's conversations.