Criteria 3.2.4 states that any items that share functionalities—icons, navigation links, etc.—are consistently named and labeled. This makes it easy for users to logically navigate and understand site structure.
An example of this criteria in practice is the guiding navigation at the bottom of this post stating, "Next Article: 3.2.5 Change on Request." Every post in this series of blogs has a similar next article link, that will consistently take you to the next article, and there will not be a circumstance where the next article function takes you to the previous post, or the homepage.
It's interesting to note that consistent does not imply identical. For example, the next article function will not always say, "Next Article: 3.2.5 Change on Request." as the posts will continue to increase, and the number variable will change.
If you are using icons, the same icon can be used differently site-wide as long as they serve separate functions and are labeled properly. For example, you can use an X icon to convey 'close' and also 'not included,' with the proper labels. however, if you were to use an X icon to convey 'close' and 'exit,' this would be a failure of the criteria as they're similar functions but inconsistent labeling.
Another note to keep in mind is that aria labels must be kept consistent across elements, or it is also considered a criteria failure.