The "Number Sign," also known as the "Hash" symbol (#), is a typographical character used in various contexts. It is commonly found in social media, where it precedes keywords or phrases to create a hashtag, allowing users to categorize and search for related content easily. In computing, the hash symbol is often used in programming languages and markup languages, such as Python and HTML, to denote comments or special functions. Additionally, it plays a role in data structures like hash tables, which are used for efficient data retrieval.