What is Reflection? How can it be used to break Encapsulation? What are the performance costs?

Reflection allows a program to inspect types and, depending on the language and runtime permissions, access members dynamically at runtime. It powers frameworks such as dependency injection, serializers, ORMs and test frameworks. Reflection can weaken encapsulation when code accesses private members through runtime metadata or bypass mechanisms. It can also have performance and maintainability costs because operations may require metadata lookup, dynamic invocation and reduced compiler optimization compared with direct calls. Modern runtimes often optimize or cache reflective operations, so the actual cost should be measured rather than assumed.