An Immutable Map is a data structure that allows you to store key-value pairs, similar to a regular map or dictionary. The key feature of an immutable map is that once it is created, it cannot be changed. This means you cannot add, remove, or modify any of the entries in the map. This property makes immutable maps useful in functional programming, where data integrity and predictability are important. When you need to make changes to an immutable map, you create a new map that reflects those changes instead of altering the original. This approach helps avoid side effects and makes it easier to track changes over time. Libraries like Immutable.js provide implementations of immutable maps, enhancing performance and reliability in applications.