A bibliography is an overview of (almost) all publications in some category:
works of some author
publications about some specific subject
publications published in some specific country
publications published in some specific period
publications mentioned in, or relevant to, a particular work (a bibliography of this type, sometimes called a reference list should normally appear at the end of any paper in scientific literature)
A bibliography tries to give a complete overview of the (important) literature in its category. This is opposed to a library catalog, which only describes items actually found in the library. However, some national libraries' catalogs also serve as national bibliographies, as (almost) all publications of this country are contained in the catalogs.
Bibliographies can be sorted in several ways, similar to library catalogs.
Annotated bibliographies give descriptions about how each source is useful to an author in constructing a paper or argument. Creating these blurbs, usually a few sentences long, establishes a summary for and expresses the relevance of each source prior to writing.
It can be divided into enumerative or systematic bibliography, which results in an overview of publications in a particular category, and analytical or critical bibliography, which studies the production of books.
Bibliographies differ from library catalogs by including all relevant publications rather than items actually found in a particular library.
Descriptive bibliography is the close examination of a book as a physical object, recording its size, format, binding, and so on, while historical bibliography takes a broader view of printing and publishing.
This chapter is concerned primarily with descriptive bibliography, especially with the terms that the book collector must master before he or she can use descriptive bibliographies intelligently and read booksellers' catalogues wisely.
Analytical bibliography may deal with the history of printers and booksellers, with the description of paper or bindings, or with textual matters arising during the progression from writer's manuscript to published book.
Unfortunately, good descriptive bibliographies do not exist for all fields and for all periods, and, as a result, collectors must frequently do their own spade work, learning enough about the techniques of descriptive bibliography to distinguish among editions, issues, and impressions without outside help.