The terms, "valid and invalid," are used frequently in the 1997 science fiction movie, Gattaca. Although they are commonly used in the outside world of Gattaca, they are used most often within the headquarters of Gattaca Aerospace Corporation.
Employees must always have to be tested for blood, urine, hair--anything that can help identify DNA, so the company always knows that it is them. As the world runs via genetics by now, most people cannot see past anyone's genetic makeup, thus making these tests in the company mandatory. Through all this, it is seen how big of a contrast there is of "valid" and "invalid".
"Valid" means that the person was born in vitro and has been genetically modified in some way. Note that just because the DNA matches, the person may not be the same. Vincent Freeman models this in the movie by borrowing the ladder of Jerome Morrow.
"Invalid" means a person that is a 'faith birth' or vitro birth, and thus has not been genetic engineered. It is often someone who is not registered within the company or someone with apparent genetic defect(such as bad eyesight). Vincent, for example, is invalid.
Easy Ways to tell if Someone is "Invalid
There are other ways to tell if someone is invalid without doing a sample. First, the company looks for employees who are generally perfect in their genetic makeup, meaning that they don't have any major problems. For instance, someone may not be "valid" if they are wearing glasses, which would indicate a genetic problem of myopia.