Which of the following steps refers to acquiring data that is stored and not being used at the moment?

Acquiring data stored but not actively in use refers specifically to non-volatile data. Non-volatile data is information that is retained even when the device is powered off, such as files on hard drives, USB sticks, and solid-state drives. This type of data is essential in digital forensics since it can provide a wealth of information regarding activities that occurred before the device was turned off.

In contrast, volatile data would pertain to information currently in use or stored temporarily in memory, which is lost when the device is powered off. Validating data acquisition involves verifying the integrity and reliability of data captured, but it does not pertain to the type of data being acquired. Sanitizing the target media involves processes to ensure that data is securely erased or made inaccessible, rather than acquiring it. Thus, the answer that correctly identifies the method of acquiring data that is stored and not actively being used is non-volatile data.