The hashtag, used to categorize a tweet within a theme, was pioneered by Twitter and is still a staple on the platform today. Hashtags were later adopted by Facebook and Instagram and can now be used to express almost anything. While some are straightforward, you may need a little help with the others. Luckily, Digimind's got you covered! Here's a mood-based guide to some of the most popular hashtags across the internet.