Accuracy
Accuracy has to do with comparing two measurements to each other. One of those measurements is the measurement you are taking with some sort of measuring tool. The second measurement is the true value of that which you are measuring. The amount of difference between these two numbers is the amount of accuracy, with smaller values being more accurate. The closer the measurement you take is to the true value of what you are measuring, the more accurate your measurement is. Accuracy is very important in precision measurement techniques because you want the numbers you are collecting to be close to the actual values you hope to get. Any deviation from accuracy in a measurement system will throw off the entire measurement process.