Velocity ratio in a mechanical context is defined as:

The correct answer, which defines the velocity ratio in a mechanical context, pertains to the Ideal Mechanical Advantage. The velocity ratio is a measure that compares the input velocity to the output velocity of a machine or mechanical system. It reflects how many units of distance the effort moves compared to how many units of distance the load moves.

In an idealized situation, the velocity ratio is calculated without accounting for losses due to friction or other inefficiencies, meaning it represents the maximum efficiency that could be obtained if a machine operated perfectly. This concept is fundamental in understanding how machines can amplify force and work, as it helps to determine how effectively they convert input energy into output energy.

The other options do not accurately represent this principle. Actual efficiency relates to the performance of a machine in real-world scenarios, taking into account energy losses. Actual mechanical advantage is a ratio that reflects the real-world gain in force from a machine, whereas the ideal mechanical advantage is purely theoretical. Velocity proportion is a more generalized term that does not specifically correspond to the technical meaning of velocity ratio in the context of mechanical advantage.