This is when several works share a name. They could even be different media. And yet they're completely unrelated.
When the names are slightly different, it might be a case of Translation Matchmaking. If the titles are identical to each other except for an added article in either ("a," "the," etc.), for instance Following and The Following, we'll count them too.
See also Recycled Title, which is when a work set in the same fictional universe uses the same title as an earlier one.
This is so prevalent that Wikipedia developed the Disambiguation system to address this and similar issues (like common surnames). So have we, actually — see the Ambiguity Index for a list.
For those unfamiliar with intellectual property laws, titles can't be copyrighted and it's totally legal to name a work with the same name as another one; however, if the title is trademarked, then you can't. Trademark covers a franchise, not a single work/series.
Care must be taken to make sure this doesn't become a militant In Name Only. This is strictly when two works just happen to share the same name, not an adaptation/sequel/remake that bears no resemblance to the previous work.
Example subpages (alphabetical by title):