An immutable object is an object whose state cannot be modified after it is created. This means that once the object is initialized with certain values, those values remain constant throughout its lifetime. In programming, this concept is often used to enhance reliability and predictability, as it prevents accidental changes to the object's data. Common examples of immutable objects include strings in Java and Python. When you manipulate these strings, you actually create a new string rather than changing the original. This property can lead to safer and more efficient code, especially in concurrent programming environments where multiple processes may access the same data.