GOM = Guess-O-Meter
Since your range fluctuates so much in an electric vehicle, your maximum range is a 'guess' based on your prior driving history.....being your average miles/kWh. The higher your average miles/kWh, the greater your range. Your GOM will try to calculate that and display it to you on the cluster, so you don't have range anxiety. Notice how ICE cars doesn't have a GOM to tell you your maximum driving range depending on how full of a tank of gas you have. The GOM is added to relieve ppl of range anxiety and to warn them that they might be low on juice depending on their usual driving habit.
Of course, the most accurate way to determine your maximum range is to just multiply your average miles/kWh to the SOC (state of charge....how full is your battery in %) to 64 (which is the usable capacity of the battery).