Explain move semantics in C++11 and when to use them.

Move semantics transfer resources from temporary objects instead of copying. Rvalue references (T&&) bind to temporaries/movable values. std::move casts to rvalue reference, enabling move. Move constructor/assignment: steal resources from source, leave source in valid but unspecified state. Benefits: avoid expensive copies of containers, strings; enable unique_ptr. Rule of Five: if you define destructor/copy, define move too. Use: returning local objects (guaranteed move), moving into containers, std::swap. Move is usually O(1) vs copy O(n). Perfect forwarding: std::forward preserves value category.