When a projector is physically positioned, depending on the angle that it is to the screen, the image projected may not be square.
Digital projectors have keystone adjustment to correct this.
A typical example would be a projector on low table, projecting onto a screen that is higher. In this instance the image would be distorted. The top of the image would be wider than the bottom and a trapezoid shape. This is easily corrected on a projector by just pressing the keystone button that shrinks the image at the top to square it up again. This is referred to as vertical keystone and is a feature on all of our projectors.
Today, even lower spec projectors have horizontal keystone too. This means that you can also correct the left and right sides of the image giving even more flexibility in positioning.
Higher spec projectors now have more advanced keystone options called Geometric Correction. For more on this, see below.