An "event" is essentially any security system information your Vista 20P automatically tracks and stores.
Events have a wide range of classifications. They can be anything from access points opening or closing, an authorized user arming/disarming the alarm system, or even a sensor or detector triggering an alarm. Granted, these occurrences differ greatly in number and severity, but all this information is useful to end users who want to keep a close eye on all the goings-on in their security network.
Event information is stored in a menu known as the event log, and can be easily accessed on the 6160 and 6160RF alphanumeric keypads.