<operating system> Sun Microsystems, Inc.'s version of the Unix operating system. As well as the core operating system, Solaris inludes networking software, the Java Virtual Machine, the CDE/Desktop that includes an X11-based windowing environment and graphical user interface.
Sun claim that Solaris is not just an operating system but an "operating environment".
Solaris 1.x was a retroactive (marketing?) name for SunOS 4.1.x (where x>=1).
Solaris 2.x (which is the first version most people call "Solaris") includes SunOS5.x, which is an SVR4-derived Unix, OpenWindows 3.x, and tooltalk.