Final answer:
4) Steady-state operation. Steady-state operation is the operation that is performed at a substantially constant load for an indefinitely long time.
Step-by-step explanation:
The operation that is performed at a substantially constant load for an indefinitely long time is called Steady-state operation.
In physics, a steady-state operation refers to a state where all the parameters of a system remain constant over time. This means that the system's output or behavior does not change even when there are variations in the input or external conditions.
For example, in an electrical circuit, steady-state operation occurs when the voltage and current in the circuit remain constant over time, despite changes in the input voltage or load resistance.