In C++, the `std::placeholders` namespace provides a way to create placeholder objects that can be used with function objects, particularly when using `std::bind`. These placeholders allow you to specify where arguments should be passed in a function call, enabling more flexible and reusable code. When you use `std::placeholders`, you can define a function with fewer parameters than the original function. For example, you can bind some arguments while leaving others as placeholders, which can be filled in later when the function is called. This is especially useful in scenarios like callbacks or event handling.