A hash sign, commonly known as a hashtag, is a symbol represented by the pound sign (#). It is used primarily on social media platforms to categorize content and make it easily searchable. By placing a hashtag before a word or phrase, users can link their posts to a broader conversation or topic, allowing others to find related content quickly. Hashtags originated on the platform Twitter in 2007 and have since become a standard feature across various social media sites, including Instagram, Facebook, and TikTok. They help users engage with trending topics, events, or themes, enhancing online communication and community interaction.