In the fields of engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of aquantity to its actual (true) value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results.^[1] Although the two words can be synonymous in colloquial use, they are deliberately contrasted in the context of the scientific method.

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Accuracy准确度 is the difference between the measured value and the true value of a tested material.

Precision精确度 is the repeatability of successive measurements under the same conditions.

测量的精密度、准确度和精确度

这是人们在测量中常常容易混淆的三个名词，虽然它们都是评价测量结果好坏的，但涵义有较大的差别。

　　1．测量的精密度高，是指偶然误差较小，这时测量数据比较集中，但系统误差的大小并不明确。

　　2．测量的准确度高，是指系统误差较小，这时测量数据的平均值偏离真值较少，但数据分散的情况，即偶然误差的大小不明确。

　　3．测量精确度（也常简称精度）高，是指偶然误差与系统误差都比较小，这时测量数据比较集中在真值附近。

Accuracy 
Accuracy is how close a measured value is to the actual (true) value. 
Precision 
Precision is how close the measured values are to each other. 
准确度（Accuracy）：指在一定实验条件下多次测定的平均值与真值相符合的程度，以误差来表示。它用来表示系统误差的大小。 
精密度（Precision）：是指多次重复测定同一量时各测定值之间彼此相符合的程度。表征测定过程中随机误差的大小。 
精确度=准确度+精密度 
可用下图表示：

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Accuracy and precision in binary classification 
"Accuracy" is also used as a statistical measure of how well a binary classification test correctly identifies or excludes a condition. 
That is, the accuracy is the proportion of true results (both true positives and true negatives) in the population. It is a parameter of the test 
On the other hand, precision is defined as the proportion of the true positives against all the positive results (both true positives and false positives)