What is the difference between accuracy and precision in measurements?

Accuracy refers to how close a measurement is to the true value - a highly accurate instrument gives readings near the actual quantity. Precision refers to how repeatable measurements are - a precise instrument gives consistent readings even if they are all offset from the true value. An instrument can be precise but not accurate (consistent but biased), or accurate but not precise (averages correct but scattered). Ideally, instruments should be both accurate and precise.