What term describes something that cannot be penetrated or permeated?

The term that describes something that cannot be penetrated or permeated is "impermeable." This word is often used in scientific contexts, particularly when discussing materials or substances that do not allow fluids or gases to pass through them. For example, a waterproof barrier is considered impermeable because it prevents water from seeping through. The concept applies to various fields, including engineering, biology, and environmental science, where understanding the permeability of materials is essential for applications such as construction and pollution control.

The other terms listed do not convey the same meaning. "Incessant" refers to something that is continuous or unending, typically in a negative context, such as noise. "Inane" describes something that is silly or lacking in meaning. "Incumbent" denotes a person who currently holds a particular position or office, often in politics. None of these options relate to the inability to be penetrated or permeated, which reinforces why "impermeable" is the correct choice.