Pitch is a measurement of how far the propeller moves forward during one full revolution.
Most boats experience some "slippage" between the blades and the water. This means that the propeller does not advance the full distance of the design pitch during each revolution. The amount of slippage varies from boat to boat.
Pitch is the second number listed in the propeller dimensions.
Pitch is the forward movement of the propeller after one revolution assuming there is not slippage.