`std::async` is a function in the C++ Standard Library that allows you to run tasks asynchronously, meaning they can execute in the background while your main program continues to run. It simplifies concurrent programming by automatically managing threads for you, returning a `std::future` object that can be used to retrieve the result of the task once it completes. When you call `std::async`, you can specify how the task should be executed, either in a new thread or using the calling thread. This flexibility makes it easier to write efficient and responsive applications, as you can perform time-consuming operations without blocking the main thread of execution.