An edited book is one that is divided into chapters, each of which is written by a different author or group of authors. 

Edited books are valuable in that the individual chapters are generally authored by specialists. Sometimes the chapters were originally published as journal articles, and are reprinted because of their enduring importance. In other cases, the editors have asked authors with differing perspectives to state their points of view on a single topic. These multiple "takes" on a single subject can be crucial in looking at a topic's broader perspective (from APA Reference Style by David S. Baker and Lynn Henrichsen).