Normally, material must be (directly) about the subject of the article. The situations below are examples of when that rule is broken. These exceptions do not have consensus as official policy.
Often accepted for establishing context
Without sufficient context, even some highly relevant information can seem to have little importance to the subject of the article. This is especially true when disparate facts are grouped together, such as in a "Trivia" list. An introductory paragraph may help convey its significance.
Often accepted for later works that have influenced the original
In many cases, a fact that connects two subjects may be important to one of the subjects, but not the other. This is commonly the case with creative works that are based on, or otherwise incorporate, other subjects: while the original subject often has importance to the referring work, only very famous references will register an impact on the original subject. Books, movies, and other works (such as documentaries or biographies) that are specifically about a subject are often relevant to that subject, especially if the work has influenced public perception of the subject in some way.
Often accepted for almanac type lists
Wikipedia is an editable encyclopedia (along with some topics that would typically be found in an almanac).— From Wikipedia help pages: "Wikipedia:Tutorial (Keep in mind)"
"Trivia" and "In popular culture" lists are the most common types of "almanac" lists, in Wikipedia. These are bullet point or numbered lists. To improve the formatting and organization of "Trivia" information, Wikipedia:Avoid trivia sections, recommends moving Trivia material into other sections as prose, adding context where possible. Sometimes a new section (or a new, more tightly-focused list) can be created out of closely-related items. However, even when a given set of information is best organized via a structured list, an introductory paragraph may help convey its significance to the subject. Incidental connections between subjects (i.e., with no demonstrable impact on either) do not need to be listed anywhere on Wikipedia.