I hope i can explain this in English, but i will give it a try.
On some (the more expensive) scopes you also have a parralax adjustment knob for different distances.
How to understand this parralax adjustment:
If you're looking straight through your scope - the reticle is right between you and the point you are aiming on.
If you moving your head a very littlebit to the right or the left (which means: not 100% straight looking through the scope) the reticle will not be exactly in the middle (between you and the aiming pont) anymore. You'r shot will be not exactly on the place you were aiming on.
In case of the more expensive scopes, which are be able to adjust this on every distance - it will be easier for you to shoot on every distance without having problems looking straight through the scope.
In this case, the scope is only made for the parralax of 30 yards.
There is some and clear good info on youtube about this. (parallax adjustment)
I hope i did explain this the right way. Some others will help me if i had made a mistake.