Immutable data refers to information that cannot be changed or modified once it has been created. This means that any attempt to alter the data results in the creation of a new version, rather than changing the original. This property is essential in various fields, including computer science and data management, as it ensures consistency and reliability. In programming, immutable data structures, such as those found in languages like Haskell or Scala, help prevent unintended side effects and make it easier to reason about code. By using immutable data, developers can create more predictable and maintainable applications, as the state of the data remains constant throughout its lifecycle.