Reliability refers to the consistency of a measure. For example, in an investigation, if a measuring device consistently produces the same results when used to measure the same quantity, it can be considered reliable.
Validity refers to the accuracy of a measure. In an investigation, if a measuring device accurately reflects the true value of the quantity being measured, it can be considered valid.
Precision refers to the degree to which repeated measurements of the same quantity agree with one another. In an investigation, if a measuring device produces results that are consistently close to one another, it can be considered precise.
For example, in an investigation to determine the weight of a substance, a reliable, valid, and precise scale would consistently produce the same weight measurement for the substance each time it is weighed, and the measurement would accurately reflect the true weight of the substance.