A hashtag is a type of label or metadata tag used on social network like Facebook, Twitter or Instagram.
Using hash tag on your post will make it easier for other users to find your post or messages among the millions of post from other users worldwide. And by attaching a hash tag on your post in social media like Twitter, you are explicitly exposing it to all users or a company who sponsors and keep track of the hash tag that you used. Think of a hash tag as a way to filter all the posted content based on a certain keyword/tag. Users can create and use hashtags by placing the hash character (or pound sign) # in front of a word or unspaced phrase.
Sample of Hashtag:
#GMAnews, #muhammadali, #hugot, #AsaPaMore
If a hash tag is used by many users on their post or comments, a hashtag can “trend” and attract more individual users to discussion. On Twitter, when a hash tag becomes extremely popular, it will appear in the “Trending Topics” area of a user’s homepage.