An MCU is a Micro Controll Unit, a central control unit similar to a computer's CPU.
CPLD is a programmable logic device, I do not know if you please out of the three-state gate, and not the gate these things, the role of CPLD is through programming, can make a CPLD chip as N multiple doors to use. It is very important when testing new product prototypes.
The term FPGA is called the field programmable gate array, which means that it has a particularly large number of logic circuits. Its purpose is similar to the MCU, but the structure is very different. The CPU reads instructions through the memory one by one, and the FPGA operates on it through the programming device (programming), which connects the logic gate according to certain laws, making it a controller with fixed functions, and the advantage is that the cost is low, the speed is very fast, and it is very stable. The disadvantage is that modifying the program is cumbersome and requires reprogramming with specialized equipment.