Refer to figure.
Induced drag is the drag which results from creating lift. In other words, the energy required to turn the air. It is absolutely linked with lift, so this type of drag is sometimes known as “Lift Dependent Drag”.

Because the lift generating components of a helicopter are the rotor blades, induced drag is specifically associated with them.

The induced drag is greatest in hover, where the pitch angle and induced airflow are at their greatest. As forward speed increases, the induced airflow decreases, increasing the effective angle of attack, so the lift required to maintain altitude becomes less, as a result the induced drag decreases.

More specifically, as shown in the figure, Induced drag varies linearly inversely proportional to the square of the airspeed (V2).