Reliability (of a tool) refers to consistency of the tool. The tool must give the same / similar results no matter how many tries / testing and retesting.

Validity is the extent to which the tool measures what it is intended to measure

standardization - making norms

validity is about the accuracy of a measure, i.e., how well it measures what it is supposed to measure. Reliability is about the consistency of a measure, i.e., how well it produces the same results under the same conditions. A measurement can be reliable without being valid, but a valid measurement is usually also reliable. For example, if you use a broken thermometer to measure the temperature of a liquid sample several times, you might get the same reading every time (reliable), but it does not reflect the true temperature of the sample (invalid). On the other hand, if you use a working thermometer to measure the temperature of a liquid sample several times, you should get the same reading every time (reliable) and it should match the true temperature of the sample (valid).


read also - accuracy vs precision