was the final release of the "Classic" Mac OS line, released in late 2001/early 2002. It served as a bridge to Mac OS X (running in "Classic Environment" mode) but was also the primary OS for many legacy PowerPC Macs.

Mac OS, originally System Software, is the line of operating systems developed by Apple for Macintosh computers. The first version of Mac OS, System 1.0, was introduced in 1984 and was notable for its graphical user interface (GUI), a significant departure from the text-based interfaces that were common at the time.