What is a memory leak? How do GC languages still leak memory?

Memory leaks

A leak is memory no longer needed but still reachable—GC cannot collect it. In GC languages: static collections, listeners not removed, unclosed streams, ThreadLocal abuse.

• C/C++: missing free / RAII with smart pointers.
• Java: cache grows forever—use size bounds or weak references.
• Profile with heap dumps / VisualVM when OOM in prod.