偏差 (piān chā) is a noun meaning 'deviation' or 'error', referring to a measurable difference between an observed value and a standard, expected, or target value. The character 偏 means 'to lean', 'to deviate', or 'to be biased', while 差 means 'difference' or 'discrepancy'. Together, they convey the idea of a departure from correctness, accuracy, or normality—often in technical, scientific, statistical, or medical contexts. It’s commonly used when discussing measurement errors, clinical test results, data analysis, or quality control.

This word carries a neutral-to-formal register and is rarely used in casual speech. It implies objectivity and quantifiability: the deviation can usually be expressed numerically (e.g., ±0.5 mm, 3%). While it may describe unintentional error, it does not imply blame—it simply signals that a value falls outside an acceptable range. In healthcare, for example, a lab result showing a 'blood glucose deviation' might prompt further testing rather than immediate diagnosis.