What Does Windows 9x (Win9x) Mean?
Windows 9x (Win9x) refers to the series of versions of Microsoft Windows released between 1995 and 2000. Windows 9x comprises Windows 95 (and the various "OS-R" updates to Windows 95, which were provided only via PC makers), Windows 98, Windows 98 Second Edition (SE) and Windows Millennium Edition (Me).
Techopedia Explains Windows 9x (Win9x)
Windows 9x differed from previous Windows versions (1.1, 2.0 and 3.0) by their device driver, virtual memory management and the MSDOS.SYS and MS-DOS kernel. A variety of fonts as well as improved graphics were a part of the 9x series. The GUI experienced a complete overhaul from its predecessors and the kernel supported bigger VFAT (virtual file allocation tables) which significantly increased the speed of the system. Moreover, file names in Windows 9x were allowed to have up to 255 characters, in contrast to previous versions which were limited to MS-DOS-style 8.3 letter filenames (up to eight letters naming the file and three as the file extension).
Windows XP's release in 2001 marked the end of the Windows 9x era.