Accuracy and precision are used in context of measurement. Accuracy is the degree of conformity of a measured or calculated quantity to its actual (true) value, while precision is the degree to which further measurements or calculations show the same or similar results. In other words, the precision of an experiment/object/value is a measure of the reliability of the experiment, or how reproducible the experiment is. The accuracy of an experiment/object/value is a measure of how closely the experimental results agree with a true or accepted value.
Both accuracy and precision are terms used in the fields of science, engineering and statistics.
Contents: Accuracy vs Precision
One can say that a measurement is accurate but not precise; precise but not accurate; neither or both. An example of bad precision and good accuracy can be: Suppose a lab refrigerator holds a constant temperature of 38.0 F. A temperature sensor is tested 10 times in the refrigerator. The temperatures from the test yield the temperatures of: 37.8, 38.3, 38.1, 38.0, 37.6, 38.2, 38.0, 38.0, 37.4, 38.3. This distribution shows no impressive tendency toward a particular value (lack of precision) but each value does come close to the actual temperature (high accuracy).
edit Target comparison
Accuracy is the degree of veracity while precision is the degree of reproducibility. Target comparison can be used to explain this difference between the two terms. If arrows are fired at a target and measurements are taken then accuracy will describe the closeness of the arrows to the bullseye at the target center. Arrows that strike closer to the bullseye are considered more accurate. The closer a system's measurements to the accepted value, the more accurate the system is considered to be. If a large number of arrows are fired, precision would be the size of the arrow cluster. (When only one arrow is fired, precision is the size of the cluster one would expect if this were repeated many times under the same conditions.) When all arrows are grouped tightly together, the cluster is considered precise since they all struck close to the same spot, if not necessarily near the bullseye. The measurements are precise, though not necessarily accurate. However, it is not possible to reliably achieve accuracy in individual measurements without precision.
edit Number of measurements
Another difference between the two can be that accuracy can be determined by one measurement while many measurements are needed to determine precision. In the above example, by just one arrow fired, one knows if it is accurate or no but a number of arrows have to be fired to know if the result is precise or no.
While a precise measurement may speak highly of an instruments quality, an accurate reading will not reflect on the quality. Accuracy is an agreement of a measured value with an expected value. Another example: A stopped clock will be accurate twice in day, but it will not be precise - a reflection on its quality. If a clock reflects the right time in 10 readings at 10 different points in time it can be considered precise and therefore of high quality.
Both Accuracy and Precision can be used in quantifying and statistics, physics, engineering and logic testing.