Hashtags are words or phrases prefixed with the symbol # a form of metadata tag. Used in messages on microblogging social networking services such as Twitter. You can use hash tags to revitalize old photos that didn't get the attention they deserved or comment on other photo with your choice of tag. Using the top Instagram Tags insures that your photo will be view-able by many who subscribe or monitor those tags. Just paste key words with the hashtag (#) prefixed in the comment section of your photo.