An FPGA is a programmable semiconductor device that can be reconfigured to perform a wide range of tasks. It is often used in applications where the specific function to be performed is not known at the time the FPGA is designed. FPGAs are faster and more efficient than general-purpose microprocessors, but less flexible than ASICs, which are designed specifically for a single task. They are more expensive than microprocessors, but offer more flexibility and can be reprogrammed as needed.