Final answer:
The term related to the efficiency of a rocket's engine is the Thrust Ratio, which reflects the efficient use of fuel to create thrust. Higher efficiency is achieved with greater exhaust velocity and rapid fuel ejection, especially in the vacuum of space.
Step-by-step explanation:
The term that refers to the efficiency of a rocket's engine is c) Thrust Ratio. The thrust ratio, also known simply as thrust, is a measure that applies to rocket propulsion and reflects the efficient use of fuel to produce movement. A rocket's acceleration and thus its thrust is influenced by three primary factors: the exhaust velocity of the gases, the rate at which mass is ejected, and the mass of the rocket itself. A key principle here is that as the fuel burns and mass of the rocket decreases, acceleration increases, with efficiency being higher when mass is ejected faster and the exhaust velocity is greater. Rockets are more efficient in outer space than in Earth's atmosphere because in space, there is no air to create frictional forces, allowing for a more effective propulsion system.