RAM and stack memory
All RAM memory requires a constant current to hold its state. That is, as soon as you turn the power off, all of your RAM memory vanishes. Thus, RAM is volatile.

The stack is a specific area of RAM memory used to store temporary variables during program execution. Each function call "pushes" data to the stack. The data is "popped" when the function returns. Because the stack is stored in RAM, it too is volatile.