Wikipedia:Wikipedia in brief

Wikipedia is a neutral and unbiased compilation of notable, verifiable facts.

This can be expanded as follows:

Neutral: Wikipedia does not judge or advocate specific views, or choose between them. Rather, it judges the value to users of neutrally representing different views.
Unbiased: Views are allowed to speak for themselves rather than being cast into one "right" viewpoint.
Compilation: Wikipedia is not a simple collection or list of facts. There is a process of summarizing, grading, organizing and collating involved, to ensure that the resulting articles are as useful as possible for readers seeking both detail and overview.
Notable: A view is generally considered notable if it is potentially information of value or interest in some way to a significant number of people, or to some perspective, or its omission would leave a significant gap in historical human knowledge of a subject. Even minority, controversial and discredited views are often notable. Often it is valuable to see how people thought, or competing views of the time. By contrast many fringe views are not notable by this definition, because they are not sufficiently significant or had little or minor impact in their field as a whole.
Verifiable: Information must be objectively verifiable, including being cited from a credible source.
Facts: Wikipedia contains facts, not opinions, and not original research. Since any opinion of note has been expressed by some person or group of people, we do not try to decide or claim that an opinion is "true" or "false". We state instead, neutrally and factually, which people hold what views, and allow the facts to speak for themselves.

For information to be included in Wikipedia, it should at a minimum be both notable and verifiable.

If it is verifiable but not notable, it is by definition below a certain threshold of importance, and will not usually merit recording, no matter how true.
If it is notable but not verifiable, it is effectively hearsay.

Unimportant matters or hearsay are usually outside the scope of Wikipedia.

If a view is both notable and verifiable, and not original research, then it may be appropriate to record it in Wikipedia, in which case:

Wikipedia:neutral point of view ("WP:NPOV") is the core policy that informs how facts must be represented and articles written.
Wikipedia:verifiability ("WP:V") and Wikipedia:cite your sources ("WP:CITE") are the twin statements explaining how verifiability should be checked and documented.
Other policies and guidelines cover ancillary matters such as appropriate user conduct, style and content, and copyright compliance.

Footnotes

Notability is a subjective decision formed by consensus of editors when they try to characterize human knowledge and history of a subject or field, in a balanced manner.
As Wikipedia:Policy trifecta points out, Wikipedia is not just an encyclopedia. it is also a wiki, and a community. This definition relates to its role as an encyclopedia.

See also

Footnotes