Sorry! Power Usage Effectiveness. It's a measure of the overhead of delivering power to the servers (or motherboards, depending on how you measure it), taken to include all other datacenter power overheads: AC/cooling, UPS losses, and sometimes transformer/rectifier losses.
A PUE of 1.2 means that for every watt of power you're using in a server, you're using 1.2 watts drawn from the grid (approximately). Those extra 0.2 watts are being spent on cooling and other things.
A PUE of 1.2 means that for every watt of power you're using in a server, you're using 1.2 watts drawn from the grid (approximately). Those extra 0.2 watts are being spent on cooling and other things.