What term describes a type of memory whose contents are retained even when power is off?

The term "nonvolatile" specifically refers to a type of memory that retains its data even when the power is turned off. This characteristic ensures that information stored in nonvolatile memory remains intact without requiring a constant power supply, making it essential for storing important data that needs to be preserved between sessions, such as firmware or configuration settings.

In contrast, other terms listed do not relate to this concept. "Umarbitrary," "nonadjacent," and "inaccessible" do not describe properties of memory in relation to power and data retention, and therefore do not apply to the context of this question. Nonvolatile memory is crucial for various applications, including hard drives, flash drives, and ROM, emphasizing its importance in computing and data management.