What is "prior art"?

In principle, any publication, regardless of the form of dissemination, qualifies as prior art. The only thing that matters is that the document was available to the public anywhere in the world before the priority date.

In fact, it is sufficient for qualifying as prior art that the information is theoretically accessible to the public at large. Moreover, the information must not be contained in a single document. If the information can be derived from a combination of documents, it can be qualified as prior art. Finally, you could even take information into account that has not been published in express terms, but that may be implied in published documents ("implicit teachings").

The more information is taken into account as prior art, the less inventions may be considered new.

You as a patent examiner have to look anywhere in the world for prior art. Here you see the variety of information you can take into account when examining novelty. This list is, however, not exhaustive.