Audio jack, headphone jack, and jack plug all refer to the same thing. The headphone jack is an electrical connector for sending analog audio signals. It is one of the features that must be present in all telephones.
Mi A2 has a wired headphone port. This means that users cannot utilize their wired headphones unless they connect over USB Type-C. Users will have to choose between charging the device or enjoying the wired headphones because it is also the charging port.