When two rules target one or more of the same products, we say that those rules have product overlap. There are two places in the app where product overlap is mentioned. The first is on the rule creation/update page, right below the products field:

In the screenshot, we see that the current rule targets the Green Apple product, and the app is showing us a warning because a different rule targets the Apples collection (meaning both rules target Green Apple).

Product overlap is not necessarily a bad thing. In fact, there are use cases, like this one, where it is required. The warning just helps ensure that the overlap is intentional.

The second place that mentions product overlap is the last column of the rules table in the app dashboard:

The Product overlap column shows the rules which have overlapping products with the rule in that row. Clicking on the column values will open a dropdown containing the list of overlapping rules.