**One-Tailed Test:** A One-Tailed Test is a statistical method used in hypothesis testing. It's a directional test that helps to determine if a set of data has a greater or lesser value than a specific value or point. The "one tail" in this test refers to testing the statistical probability in one direction or 'tail' of the distribution, instead of both. This test is often employed in business A/B testing scenarios or scientific research where one is only interested in whether a parameter is either greater or lesser than a baseline, not simply different.