Which term describes the characteristic of objects in object-oriented programming where objects cannot be altered from outside?

Encapsulation is the term that describes the characteristic of objects in object-oriented programming where the internal state of an object is protected from being directly modified from outside its class. This is achieved by restricting access to the object's internal data and allowing it to be modified only through well-defined methods, often referred to as getters and setters. By encapsulating data, the object's integrity is maintained, ensuring that any changes to its state adhere to the rules defined within the class itself.

This characteristic promotes data hiding, which enhances security and makes the code easier to maintain and understand. The other terms reflect different concepts within object-oriented programming: inheritance relates to deriving new classes from existing ones, abstraction focuses on exposing only the essential features while hiding the complexities, and polymorphism allows methods to do different things based on the object it is acting upon.