Devices that behave like a wireless client may be called a station. When the Yardian is under station mode, it means that the Yardian maybe connected to a wireless router.
The AP mode is short for Access Point mode. It is one of the most common mode for all wireless routers. When Yardian is under AP mode, it means that Yardian acts as a wireless router with SSID. Your cellphone will be able to connect to Yardian when it is under AP mode.