Arial Unicode MS is a "large" font created by Microsoft in the 1990s to provide for use of multiple scripts. It has not been updated in recent years.
"The font Arial Unicode MS is a full Unicode font, containing all of the approximately 40,000 alphabetical characters, ideographic characters, and symbols defined in the Unicode 2.1 standard. Because of its considerable size and the typographic compromises required to make such a font, Arial Unicode MS should be used only when you can't use multiple fonts tuned for different writing systems." (from the archived font download page; NB, the Unicode standard is in version 5.0 as of early 2007)
"The file size of the Arial Unicode MS font is 22 MB because it is a complete Unicode font. It contains all the characters in Arial plus full fonts for Japanese, Chinese, Korean, Arabic, and Hebrew, plus all of the different symbol characters and character ranges." (from "Description of AUMS font, 2002)
Arial Unicode MS is supplied with some Microsoft Windows products but no longer available for downloading, nor is it available for separate purchase. [verify]