Wikipedia determines the notability of a topic (or its "worthiness of note") based how much significant coverage the topic has received in reliable sources that are independent of the subject to allow a comprehensive article on the topic to be written that meets all of Wikipedia's core content policies.
"Significant coverage" addresses the topic directly and in detail, so that no original research is needed to extract the content. Significant coverage is more than a trivial mention, but it does not need to be the main topic of the source material.
The book-length history of IBM by Robert Sobel is plainly non-trivial coverage of IBM.
Martin Walker's statement, in a newspaper article about Bill Clinton,[1] that "In high school, he was part of a jazz band called Three Blind Mice" is plainly a trivial mention of that band.
"Reliable" means that sources need editorial integrity to allow verifiable evaluation of notability, per the reliable source guideline. Sources may encompass published works in all forms and media, and in any language. Availability of secondary sources covering the subject is a good test for notability.
"Sources"[2] should be secondary sources, as those provide the most objective evidence of notability. There is no fixed number of sources required since sources vary in quality and depth of coverage, but multiple sources are generally expected.[3] Sources do not have to be available online or written in English. Multiple publications from the same author or organization are usually regarded as a single source for the purposes of establishing notability.
"Independent of the subject" excludes works produced by the article's subject or someone affiliated with it. For example, advertising, press releases, autobiographies, and the subject's website are not considered independent.[4]
Topics that are demonstrated to be notable based on consensus may, but are not required to, have a standalone article. Topics that are not notable typically do not have their own standalone articles but may be covered in context of other notable topics. If a topic does not meet these criteria but still has some verifiable facts, it might be useful to discuss it within another article.
Because it is difficult to fully ascertain the extent of the significant coverage for a topic from the onset, Wikipedia uses various indicators to presume the notability of a topic and allow a standalone article to be created. This gives the opportunity for editors to collaborate and expand on the article to find additional sources and expand on the coverage as to better demonstrate the topic's notability towards the expectations of WP:NOTEDEF.
The general notability guideline (GNG) is the most common indicator for the presumption of notability. If a topic has received a minimum amount of significant coverage in reliable, secondary sources independent of the subject, it is presumed notable for a standalone article.
"Minimum amount" of coverage is based on consensus, and should reflect sourcing that is sufficient to show that that the topic has some type of importance, and not simply part of routine or mention-in-passing reporting. Enough sourcing and coverage for the topic should exist to be able to expand the starting article beyond a few sentences.
"Presumed" means that significant coverage in reliable sources creates an assumption, not a guarantee, that a subject merits its own article. A more in-depth discussion might conclude that the topic actually should not have a stand-alone article—perhaps because it lacks significant coverage after thoroughly evaluating sources, or may violate what Wikipedia is not, particularly the rule that Wikipedia is not an indiscriminate collection of information.[5]
^Including but not limited to newspapers, books and e-books, magazines, television and radio documentaries, reports by government agencies, and academic journals. In the absence of multiple sources, it must be possible to verify that the source reflects a neutral point of view, is credible and provides sufficient detail for a comprehensive article.
^Lack of multiple sources suggests that the topic may be more suitable for inclusion in an article on a broader topic. It is common for multiple newspapers or journals to publish the same story, sometimes with minor alterations or different headlines, but one story does not constitute multiple works. Several journals simultaneously publishing different articles does not always constitute multiple works, especially when the authors are relying on the same sources, and merely restating the same information. Similarly, a series of publications by the same author or in the same periodical is normally counted as one source.
^Works produced by the subject, or those with a strong connection to them, are unlikely to be strong evidence of notability. See also: Wikipedia:Verifiability#Questionable sources for handling of such situations.
^Moreover, not all coverage in reliable sources constitutes evidence of notability for the purposes of article creation; for example, directories and databases, advertisements, announcements columns, and minor news stories are all examples of coverage that may not actually support notability when examined, despite their existence as reliable sources.