When developers use custom code and gauges for their more complex aircraft, they often do not use Simconnect Events and Variables and this means you cannot use normal flight simulator software and utilities to map the custom code and gauges to your hardware.
However an aircraft developer will often use hidden Variables and their own Events, know as Custom Events to make the aircraft work. These hidden variables are known as Local Variables or Lvars for short.
Custom Events appear the same as Simconnect Events, however they only have an ID (a unique number) and never a description.