Precision:

The precision of a measurement system, also known as reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results. Although the two words can be synonymous in colloquial use, they are contrasted deliberately in the context of the scientific method.

 Accuracy indicates proximity of measurement results to the true value, precision to the reproducibility or repeatability of the measurement. A measurement system can be precise but not accurate, accurate but not precise, neither, or both.

A measurement system is called as valid system if it is precise and accurate both. Related terms are error and bias respectively.

The terminology is applied to indirect measurements, which means that, values obtained by a computational procedure from observed data.

In addition to precision and accuracy, measurements may have a measurement resolution, which is the smallest change in the underlying physical quantity that produces a response in the measurement. Its precision, but, may be low.

Precision and recall are 2 extensively used statistical classifications.

Precision can be seen as a measure of exactness or fidelity, whereas Recall is a measure of completeness

In a statistical classification task, the Precision for a class is the number of true positives divided by the total number of elements labeled as belonging to the positive class. Recall in this context can be defined as the number of true positives divided by the total number of elements which actually belong to the positive class.