No two pages can have the same title. A name conflict arises when two or more definitions or theorems in mathematics have the same name or a very similar name. This is typically encountered when one wants to create a new page. Depending on the issue, different solutions exist:
This page aims to clarify when to apply which.
Theorems with the same name always have to be disambiguated. This occurs most often when theorems are named after a mathematician, in which case the disambiguation page will look like, for example, Cauchy's Theorem.
It may occur that theorems have a different but very similar name, for example when they are named after mathematicians whose names differ only slightly. In this case it is best to add a not to be confused with hatnote at the top of each page involved.
Example: Gauss' Lemma (Polynomial Theory)
If definitions with the same name are unrelated, they have to be disambiguated. If they are related, but it requires some advanced mathematical knowledge to understand how, they have to be disambiguated as well. The difficult cases are those of 'obviously' related definitions.
Definitions that define the same thing in the same context, are treated as described in Help:Multiple Definitions, where you find more details on what is meant by same thing and same context.
Naturally, combinations of the above types of name conflicts may occur: two unrelated definitions with the same name can both have generalizations. In such a case, the generalizations are best added as subitems in the disambiguation page. This way, visitors that strand on the disambiguation page can quickly find the precise definition they're looking for in the list.