The function std::copy_if is part of the C++ Standard Library, specifically within the algorithm header. It allows you to copy elements from one range to another based on a specified condition. You provide a source range, a destination iterator, and a predicate function that determines which elements to copy. Only the elements that satisfy the condition defined by the predicate are copied to the destination. This function is useful for filtering data while copying, making it efficient for tasks like extracting specific values from a collection. The syntax typically involves iterators for the source and destination, along with a lambda function or a function pointer as the predicate.