Asio is a cross-platform C++ library, see https://think-async.com/Asio/. It provides a consistent asynchronous model using a modern C++ approach.
The ESP-IDF component ASIO has been moved from ESP-IDF since version v5.0 to a separate repository:
To add ASIO component in your project, please run idf.py add-dependency espressif/asio
The documentation can be found on the link below: