The 'ExpectedConditions' class in Selenium is a utility class that provides a set of predefined conditions that can be used to wait for a certain condition to be met before proceeding with the next step in a test. These conditions can be used in conjunction with the 'WebDriverWait' class to wait for elements to be visible, clickable, or to have a certain text, among other things.
For example, the 'ExpectedConditions.visibilityOfElementLocated(By.id("elementId"))' can be used to wait for an element with a specific ID to be visible on the page. The 'WebDriverWait' class can then be used to wait for this condition to be met before interacting with the element. This helps to ensure that the element is present and visible before the test interacts with it, which can help prevent errors and improve the stability of the test.