The HMI (Human-Machine Interface) is one part of a typical industrial control system. The HMI is the set of screens that a plant operator actually sees on his/her computer. They relay important information about the plant's operating status including alarms. The operator can also send commands to the plant hardware through the HMI screens. Behind the HMI screens is a Process Database. The Process Database holds links to the data used on the screens. Most HMIs also include support for historical trending of data.
Some major HMI development software packages are:
Intellution Fix32
Intellution iFix
Wonderware FactorySuite
Rockwell Software RSView
USData FactoryLink
Also referred to as MMI (Man-Machine Interface) and OMI (Operator-Machine Interface).