Hypothesis testing is a statistical method used to make inferences about a population based on sample data. In hypothesis testing, a researcher formulates two competing hypotheses - the null hypothesis (H0), which suggests no effect or no difference, and the alternative hypothesis (Ha), which suggests there is an effect or difference. The researcher then collects data and calculates a test statistic to determine whether the observed data provides enough evidence to reject the null hypothesis in favor of the alternative hypothesis. Hypothesis testing helps researchers make conclusions about the population based on sample data and assess the significance of their findings.