`std::partition` is a function in the C++ Standard Library that rearranges the elements of a container based on a specified predicate. It divides the container into two groups: elements that satisfy the predicate and those that do not. The order of elements within each group is not guaranteed, but all elements satisfying the predicate will appear before those that do not. This function is part of the `algorithm` header and operates in linear time, making it efficient for large datasets. It is commonly used with containers like `vector` or `list`, allowing developers to easily filter elements based on custom conditions.