Message-Digest Algorithms are cryptographic functions that take an input (or message) and produce a fixed-size string of characters, which is typically a sequence of numbers and letters. This output, known as a hash value or digest, uniquely represents the input data. Even a small change in the input will result in a significantly different hash, making these algorithms useful for verifying data integrity. These algorithms are commonly used in various applications, such as digital signatures, password storage, and data integrity checks. Popular examples include MD5, SHA-1, and SHA-256. They help ensure that data has not been altered during transmission or storage.