What does "STAGE" of a turbine mean?
The stage of a turbine can be compared to a fan moving an air flow. When speed increases, the air flow is also increasing. Let us assume that the fan speed is at the maximum. How can we further increase the flow? By adding a second fan near the first one so that it can work in sequence with it, thus doubling the flow. The more stages you add, the more air flow is developed.