Define "thermal conductivity."

Thermal conductivity is defined as the ability of a material to conduct heat. This property quantifies how efficiently heat energy is transferred through a given material when there is a temperature difference across it. Materials with high thermal conductivity, such as metals, allow heat to pass through them quickly, while materials with low thermal conductivity, like wood or insulation, resist heat flow. This concept is crucial in various applications, such as engineering, construction, and manufacturing, where managing temperature and heat loss is important.

The options related to a material's capacity to expand under heat, its ability to insulate, or the rate of heat lost from a system all focus on different aspects of thermal behavior but do not accurately capture the specific meaning of thermal conductivity as a measure of heat transfer ability.