FPGAs (field programable gate arrays) are chips comprised of simple logic functions such as AND/OR/NOT interlinked with 'gates' that can be modified, rather link in a memory chip. By chosing which of these gates are open and which closed, a FPGA can be programmed to perform patterns of logic operations almost aas fast as if they had been hard coded into the logic.
Used on Chap. 7: page 145