It looks like your machine has APC drivers/software installed and is connected to an APC UPS.
AVR stands for Automatic Voltage Regulation, where the UPS basically either reduces (AVR Trim) or increases (AVR Boost) the input voltage depending on the input coming from the power source (outlet).
It looks like the UPS is not receiving sufficient voltage at times, and the UPS software is telling you this by logging an event to the event log.
You can either ignore this warning or have your electrician take a look.
More info: http://www.apc.com/site/support/us/en/faq/?page=content&country=ITB&lang=en&locale=en_US&id=FA156554&redirect=true