Neutral point-of-view (or NPOV) means content is written objectively and without bias, merely presenting the facts and notable viewpoints of others. Encyclopedias are inherently written in this way as the truth is often subjective, and it would make no sense to have an article that favored a particular viewpoint. This also helps prevent articles becoming mere advertisements or propaganda by vested parties.
Verifiability means that articles should only contain material that has been published by reliable sources. All content should ideally be supported by a reliable source, but content that is controversial or likely to be challenged will definitely require them! Unsourced material may be removed at any time and it is the obligation for the editor adding material to provide a reliable source.
No original research means that articles may not contain previously unpublished arguments, concepts, data, opinions, or theories. This includes any new analysis or synthesis of these facts. Basically, Wikipedia is a record of human knowledge, viewpoints and summaries that already exist and are expressed elsewhere.
