NOR flash memory is one of the two popular types of flash memory. The other is the newer NAND flash memory.
Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed. Non-volatile means that no power is needed to maintain the information stored on the chip.
Flash memory is a technology that is primarily used in memory cards and USB flash drives as solid state storage and its main purpose is an inexpensive way of storing or transferring data between computers and other digital products. It's used as primary storage memory on various portable devices due to its low cost, compact size, high physical endurance and low power consumption.
What type of FLASH (NAND or NOR) is used on microcontoller?
Undoubtly, for program memory, the memory of choice is NOR Flash. NAND flash has several issues that make it unsuitable for program storage (NAND has to be accessed in blocks and has the bad habit of corrupting some of its data, so a management system is needed to keep track of blocks usage and of bad records. You don't want to put your program on an unreliable media).

