A hash function is a mathematical algorithm that transforms input data of any size into a fixed-size string of characters, which is typically a sequence of numbers and letters. This output, known as a hash value or hash code, uniquely represents the original data. Hash functions are widely used in computer science for tasks like data integrity verification and password storage. One key feature of hash functions is that they are designed to be one-way, meaning it is nearly impossible to reverse-engineer the original input from the hash value. Additionally, even a small change in the input will produce a significantly different hash, ensuring that similar inputs yield distinct outputs. Hash functions are essential in various applications, including cryptography, data structures, and digital signatures.