Wikipedia:Wikipedia in brief

Wikipedia aims to be a neutral compilation of verifiable, established facts.

This means:

Neutral: Wikipedia does not judge or advocate specific views or opinions, or make determinations on "correctness". Where differing views exist, they are presented objectively, without bias or undue weight. Balance derives from reliable sources, not personal judgment.
Compilation: Wikipedia is an encyclopedia, consisting of articles written in a particular style. There is a process which advances articles to our goal.
Verifiable: Information must be realistically verifiable by others. This is generally done by citing from reliable sources.
Established: Original ideas, interpretations, or research cannot be verified, and thus are inappropriate for Wikipedia. Wikipedia is not a primary source; it strives to be a tertiary source.
Facts: Wikipedia documents facts; it does not offer editorial opinions. Articles state the important views which exist, and who holds them ("facts about opinions").