The core operating system is called SunOS, and the addition of network services like NIS and NFS and the X Window system makes up Solaris which is numbered 2.x following SunOS 5.x up until 2.6. After that Sun dropped the "2." to lessen the confusion and just called it Solaris 7 (based on SunOS 5.7). From Solaris 8 it started to contain more and more open source software to make it easier on the sysadmin. Solaris 9 comes with OpenSSH, bash, Apache, Sendmail, BIND, gzip(1), zip, logrotate and most other stuff we used to add.
See the RosettaStone