A flash memory is a storage memory which is nonvolatile and does not have any moving parts. It is called as «Flash» because the memory blocks can be erased in a single action. The read and write operations are extremely fast in flash memory, since it has no seek time. A flash array is a collection of flash memory, which contains no moving parts. Since it contains no moving parts, it produces less heat and it has less chances of failing.
Flash arrays can transfer data to SDD much more faster than to hard drive.
The problem with flash array is that they are very, very expensive, but they deliver an amazing performance.