(taken from Wikipedia)
4.3BSD was released in June 1986. Its main changes were to improve the performance of many of the new contributions of 4.2BSD that had not been as heavily tuned as the 4.1BSD code.
After 4.3BSD, it was determined that BSD would move away from the aging VAX platform. The Power 6/32 platform (codenamed "Tahoe") developed by Computer Consoles Inc. seemed promising at the time, but was abandoned by its developers shortly thereafter. Nonetheless, the 4.3BSD-Tahoe port (June 1988) proved valuable, as it led to a separation of machine-dependent and machine-independent code in BSD which would improve the system's future portability.
4.3BSD-Reno came in early 1990. It was an interim release during the early development of 4.4BSD, and its use was considered a "gamble", hence the naming after the gambling center of Reno, Nevada. This release was explicitly moving towards POSIX compliance, and, according to some, away from the BSD philosophy (as POSIX is very much based on System V, and Reno was quite bloated compared to previous releases). Among the new features was an NFS implementation from the University of Guelph.
The files here come from the 4.3BSD-Reno area of the Unix Archive, and were donated by Rick Copeland and Kirk McKusick.
For more information about 4.3BSD, see Twenty Years of Berkeley Unix by Kirk McKusick.