What is the term for the oven-dry density at optimum moisture content?

The term for the oven-dry density at optimum moisture content is referred to as maximum density. This terminology is key in understanding how materials, particularly aggregates, behave under different moisture conditions during compaction.

At optimum moisture content, the material reaches its highest density due to the ideal balance of moisture that allows for maximum particle packing and minimal air voids. This density is typically identified during compaction tests, such as the Proctor test, where the moisture content is adjusted to find that peak density. It's important for engineers and technicians to understand this concept as it plays a crucial role in achieving the desired strength and stability for construction materials.

The other options represent different concepts or states of density that do not specifically relate to the oven-dry condition at the optimal moisture level for compaction. Understanding that maximum density corresponds to the best packing of the material under favorable moisture conditions helps clarify why it's the correct choice.