False-positive means the test result came out “positive,” indicating you have that condition, but it was wrong. Vice versa with false-negative: it looks like you don’t have the disease, but the test was wrong, so you really do. It’s not that the lab or radiologist made a mistake with the blood test or x-ray. Rather, many tests are simply not 100% accurate, through nobody’s fault. So when a test is “positive” or “negative,” we clinicians to use our judgment, & consider all information.
For this reason, sometimes it’s better not to do tests! See topic Why Not to Test People for Unlikely Conditions.