Target Disk Mode - Computer Definition
A feature used to transfer files between two Macs directly cabled via FireWire or Thunderbolt. Booting one of the Macs with the T key held down starts the computer in Target Disk Mode (TDM), and its drives appear on the desktop of the other Mac (the host Mac). Files can be dragged and dropped without permissions. When the transfer is completed, the user ejects the TDM drives on the host Mac. See Target Display Mode.