What does CTD stand for?

Conductivity

The rate at which heat is transmitted through a material. The ability of a substance to transmit heat, light or electricity. Aluminum has high electrical and thermal conductivity, making it useful in a wide range of electrical and heat-exchanging applications. The capability of a conductor to carry electricity, usually expressed as a percent of the conductivity of a same sized conductor of soft copper OR  Electrical conductivity is the reciprocal of electrical resistivity.