Raymond distinguishes between two ways of managing a software project: the traditional "Cathedral" way, and the novel "Bazaar" way.
In the Cathedral way, the software is developed by a limited number of developers, released only when being very stable, and maintained without too much help from the outside.
In the Bazaar way, the software is released very often (often in a buggy state), tasks are delegated and contributions from the outside are welcome and often.
ESR attributes the "invention" of the Bazaar way to Linus Torvalds who used it to develop the Linux kernel, a core component of a critical system - the GNU/Linux operating system. (albeit acknowledges that it was used before for other projects)
In "the Cathedral and the Bazaar" he documents his experiences in developing and maintaining his own project Bazaar-style: the fetchmail POP-retrieval system.