Referring to a complete system replacement. The term originated in days of yore, when mainframe computers and PBXs were so big and heavy that it literally took a forklift to remove an obsolete system from the computer room or switch room and replace it with another, usually of at least equal size and weight. See also heavy metal, mainframe computer, and PBX.
A major change in IT infrastructure, which generally includes new hardware and software, as well as a considerable amount of training. The term dates back to the 1960s when computers weighed several hundred pounds and actually required a forklift to move them. See upgrade.