`std::unique_ptr` is a smart pointer in C++ that manages the lifetime of a dynamically allocated object. It ensures that there is only one `unique_ptr` instance pointing to a specific object at any time, which prevents memory leaks by automatically deallocating the memory when the `unique_ptr` goes out of scope. Unlike regular pointers, `std::unique_ptr` cannot be copied, but it can be moved, allowing for ownership transfer. This feature makes it useful for resource management in modern C++ programming, promoting safer and more efficient memory handling practices while reducing the risk of dangling pointers and double deletions.