A phantom load refers to the concept that some electronics, when not specifically powered on, still draw electricity when not in use. The best way to locate these phantom loads is with a tool called a Kill-A-Watt meter.
A kill-a-watt meter can be had for around $20 and plugs into the electrical socket at the wall, then the appliance plugs into the kill-a-watt meter. The meter gives you lots of useful information including how much power the appliance is using when on or off and the cost of running the appliance (after inputting estimated electric cost).
If a kill-a-watt meter is not an option, a good rule of thumb is that anything that has a light that is on when the device is off is using electricity. These devices can be unplugged, or more simply plugged into a power strip that can be switched off. There are even smart power strips that sense when the device attached to the single master is on or off. The strip removes, or supplies, power to all of the other outlets in conjunction with the state of the master outlet.
To learn more about phantom loads, view this video.