Bende,
Patrick correctly stated what hydration is from a baker's percent standpoint, and Bill gave the recommended hydration for a typical all-purpose flour. If you are using a good digital scale and weighing the flour and water, your hydration will always be at the proper percent. However, if you are using volume measurements, the hydration can swing quite widely in either direction, depending on how you measure out the flour, that is, with a light hand or a heavy hand or something in between.
Peter