Pitch is a measurement of how far the propeller moves forward during one full revolution -assuming there is no "slippage" between the propeller blade and the water.
For most boats, there is slippage and therefore the distance advanced is less than the design pitch. The amount of slippage varies from boat to boat.
Pitch is the second number listed in the propeller description.
Pitch is the forward movement of the propeller after one revolution assuming there is not slippage.