Proceedings are the collection of academic papers that are published in the context of an academic conference. They are usually distributed as printed books after the conference has closed. Proceedings contain the contributions made by researchers at the conference. They are the written record of the work that is presented to fellow researchers.
The collection of papers is organized by one or more persons, who form the editorial team. The quality of the papers is typically ensured by having external people read the papers before they are accepted in the proceedings. This process is called reviewing. Depending on the level of the conference, this process including making revisions can take up to a year. The editors decide about the composition of the proceedings, the order of the papers, and produce the preface and possibly other pieces of text. Although most changes in papers occur on basis on consensus between editors and authors, editors can also single-handedly make changes in papers.
Since the collection of papers comes from individual researchers, the character of proceedings is distinctly different from a textbook. Each paper typically is quite isolated from the other papers in the proceedings. Mostly there is no general argument leading from one contribution to the next. In some cases, the set of contributions is so coherent and high-quality, that the editors of the proceedings may decide to further develop the proceedings into a textbook (this may even be a goal at the outset of the conference).
Proceedings are published in-house, by the organizing institution of the conference, or via an academic publisher. For example, the Lecture Notes in Computer Science by Springer Verlag take much of their input from proceedings. Increasingly, proceedings are published in electronic format on CD only, or distributed on Internet.
A number of academic journals also use this name in their title, for example, Proceedings of SPIE, although the scientific quality of publications in proceedings usually is not so high as that of international scientific journals.