I am not a system validation expert, I'm hoping somebody from the community can update this appropriately. System Validation is used in highly regulated environments like those found in the life sciences. When creating new drugs it must be possible to recreate the exact set of circumstances for every activity related to the manufacturing process. Validation is the set of tests that assure using a specific setup and a defined set of input, the exact output will be prescribed ... in other words, it might describe the set of administrative configuration screens and their field inputs that will be seen during installation.

This excruciatingly detailed testing allows the FDA to sanction the process around drug making (if the computer system provides an incorrect answer in a validated system then the answer comes from a mistaken idea / understanding of the process not because the computer system didn't perform the way it was intended).