The Guinness book of World Records is known as such in the USA. It is known as the "Guinness book of Records" or "Guinness World Records" in other countries, but they all refer to the same publication.
The Guinness book of World Records is a collection of records. It collects things like world records in sports etc, but also a series of the wackiest records imaginable - such as longest hair growing out of somebody's ear (10.2 cm / 4 inches), the smallest wine-glass in the world (2.750 nanometres across - 20,000 times smaller than a regular wineglass) and the biggest baby ever born (10.8 kg / 23 lb 12 oz).
The Guinness Records™ history began in 1951, when the managing director of the Guinness brewery (yes, that's the black beer ("Stout") brewed in Dublin, Ireland), Sir Hugh Beaver (can anyone say "unfortunate name"?) was out hunting, and was discussing if the Golden plover or the Grouse was the fastest bird in Europe. After researching the question, he discovered that he was right, but also that there were very few resources that covered these type of things - and suggested to compile a book of all sorts of records in the world.
The first edition of the Guinness Book of World Records™ was printed in August 1955, and was the most-sold book in Britain by Christmas of that year.
After its inception, the book rapidly grew to world fame - and quickly broke a record of its own: It has sold more than 100 million copies, in a hundred different countries, in 37 different languages: The best ever selling non-religious book in the world! The book is now published in a revised edition every October - in order to coincide with christmas sales every year.
The records in the Guinness Book of World Records™ are closely fact-checked to make sure that the records are compatible (i.e that the records were set using the same standards), valid (i.e that there was no cheating involved) and useable. Because of this, the Guinness Book of World Records™ is generally seen as the most accurate collection of records in the world.
The various editions of the book aren't complete collections of all the records: every year, a new selection of records is published, and the choice is reflected by the year that has gone by per the previous edition. That way, the book is worth buying every year (great business move!), and contains "new" facts every year. If you want to settle a dispute, the web-site comes in useful, as it has a fully searchable index of its approximately 45,000 world records on file.
If you want to try and set a world record, there are a set of guidelines publised by the Guinness World Records company on their web-site (http://www.guinnessworldrecords.com - but be warned, as of November 2004, the web-site is positively horrendous)