What do those words mean?

The PCM in your truck is a computer. There is special memory in this computer that stores the programming and will retain the program while the power is off. This memory can have a new program loaded via the serial port under your steering wheel. A Tech II is required to load the factory program, predators, hypertech's and other save the factory program via this port an then load the "tunes". The act of loading the program is called flashing. Probably because it is store in a flash memory chip.

Jim