Immutability refers to the state of being unchangeable or unalterable. In software development, it often refers to immutable data structures or objects. When something is deemed "immutable," it means that once it's created, it cannot be modified.
Immutable data is emphasized in programming languages such as functional programming to ensure that once data is created, it cannot be inadvertently changed. Instead of modifying existing data, immutable structures create new data by making copies of existing data with the desired modifications. This often facilitates writing safer and more error-resistant code, as there's less room for unexpected side effects or unintended alterations.