Volatile memory
Memory or storage whose contents are erased when the system's power is turned off or interrupted. For example, RAM is volatile, if the computer was to be turned off anything stored currently in it would be erased. Because of RAM's volatile nature users must frequently save their work to a permanent medium, such as a hard drive, which is non-volatile to avoid losing data if the system's power is interrupted.
Also see: Dynamic storage, Memory definitions, Non-volatile memory