Statistical significance (p-value)

The level of statistical significance is often expressed as a p-value between 0 and 1. The smaller the p-value, the stronger the evidence that you should reject the null hypothesis. A p-value less than 0.05 (typically ≤ 0.05) is statistically significant.

Source: SimplyPsychology

Read more of statistical significance, p-values and hypotheses testing from the Beginning Statistics, Chapter 8, Testing Hypotheses.

There is also a chapter regarding the hypohesis testing in Online Statistics Education (David M. Lane): Logic of Hypothesis Testing