Water is forcefully sprayed inside the dishwasher in order to scrub the dishes clean. Some of that spray hits the door. It is important that the door seal be in good condition to prevent leakage around the door.
If the door leaks water, it may be the position of an item loaded in the dishwasher. It may result in water being deflected, resulting in a leak. If your dishwasher does not always leak, the problem may be in the way you load it. Refer to the manufacturers instructions for proper loading of the dishwasher.
The door seal may be attached to the door or the cabinet. In most cases, it will have two parts, one piece along the bottom edge and a continuous piece around the other three sides. There may also be two corner flaps on either side of the bottom rack.
The door seal parts should all be smooth, supple and free of cracks or tears. Run your finger along the seal to feel for irregularities.
If you find any damage or voids in the door seal, you will need to replace the seal.