Alarms and Events
Alarm: Alarms represent warnings of process conditions that could cause problems, and require an operator response.
Example can be many, like suppose a Tank water level has increased beyond the desired value and that time SCADA system should give Alarm.
The intention of an alarm is to signal that something has gone wrong, or that a particular stage of processing has been reached. For example, an alarm might indicate that a boiler has exceeded a safe temperature limit.
Event: Events represent normal system status messages, and do not require an operator response. An event is defined as a detectable occurrence, which may or may not be associated with an alarm.
Simple example of Event in Industrial automation can be simple logging of Operator with his user name to the SCADA application. The SCADA system can log that event in text file if configured to do so.