Destructor
A function that runs when an object is destroyed — releases resources (file handles, sockets, memory). Opposite: constructor.
C++ ~ClassName(), Rust Drop trait, Python __del__ (unsafe, runs at GC time), C# Dispose/IDisposable + using. Java's finalize() is deprecated — use try-with-resources instead. RAII (Resource Acquisition Is Initialization) is the C++ pattern tying resource lifetime to object lifetime — powerful against resource leaks.