RAM is commonly refered to as "General Purpose Registers".
That's the area where all the variables are placed.

Theoretically, you can read or write to RAM every microsecond until the end of time (or the end of the chip, which ever comes first).

The Flash area is where the program is stored. And the EEPROM is just a place to store periodically changing values that retain their data when power is removed.

RAM loses it's data when power is removed.

hth,