Stephanie Glen disambiguates three commonly confused but quite different terms:

In a nutshell, here are the definitions for all three.

1.

Significance level:In a hypothesis test, the significance level, alpha, is the probability of making the wrong decision when the null hypothesis is true.

2.Confidence level:The probability that if a poll/test/survey were repeated over and over again, the results obtained would be the same. A confidence level = 1 – alpha.

3.Confidence interval:A range of results from a poll, experiment, or survey that would be expected to contain the population parameter of interest. For example, an average response. Confidence intervals are constructed using significance levels / confidence levels.

Read on for several examples and more elaboration.