**Significance Level:** The significance level, often denoted by the Greek letter alpha (α), is a threshold that a statistical test must exceed to be considered statistically significant. It's a probability value that determines whether you should reject or fail to reject the null hypothesis in a hypothesis testing. In simpler terms, it's the probability of rejecting the null hypothesis when it is actually true, thus leading to a type I error. Commonly used significance levels are 0.05 (5%) and 0.01 (1%).