From Wikipedia's Article on Basic Role Playing
In 2004, Chaosium published the Basic Roleplaying monographs (the hyphen was dropped in the later products). Books with a quick and inexpensive printed format of tape binding and printed cardstock covers, the four monographs (Players Book, Magic Book, Creatures Book, and Gamemaster Book) were printed in order to assert Chaosium's copyrights in the run-up to the publishing and distribution of Deluxe Basic Roleplaying, a game system that is essentially RuneQuest 3rd Edition but with additions to allow play in other genres.
Chaosium released a new version of BRP on June 24th, 2008 as single comprehensive book. Currently they are selling both a printed and pdf version of the game.
Source: Wikipedia Basic Role-Playing
available under the CC-BY-SA License.
Basic Gamemaster replaced this monograph.
These monographs were to ensure Chaosium maintained the Basic Roleplaying trademark while the company worked on the subsequent 400 page softcover. They were essentially the books of third edition RuneQuest with the serial numbers filed off. In other words, all mention of Runequest as well as all of the artwork have been removed.
The artwork for the front cover is from Chaosium's abandoned Straits of Chaos project for Elric! and Stormbringer (5th Edition).