Definition of Confidence Level:
Expressed as a percentage, the confidence level indicates the probability that the value of a parameter falls within a specified range (known as the confidence interval). It characterizes your certainty about a conclusion.
For example, consider that you are sampling the width of widgets off Production Line A. If your confidence interval is 3 cm, plus or minus 0.1 cm, then at a 95 percent confidence level, you are 95 percent certain that the width of any widget you sampled from Production Line A would fall within the range of 2.9 cm to 3.1 cm. (A 95 percent confidence level is the level that is commonly used by researchers.) At a 98 percent confidence level, you are 98 percent certain, and so on.