HMI stands for Human Machine Interface. This is the interface between the operator and the controller. The HMI is the controller operating panel which comprises of a numeric keypad and a LCD screen that displays text. The keypad is used to input data into the application, such as Timer values.
The PLC's Display screen can show operator messages, variable information from the program and system information; HMI messages are created in the Display Editor and Variable information fields are created in the Variable Editor.