Traditionally each character set, such as Cyrillic, Greek or Japanese, has it's own encoding or set of alternative encodings with Latin characters added for convenience. What a numeric value stands for varies with the encoding so that the same value can stand of a Cyrillic or Greek or other character. A new encoding, Unicode, attempts to fold all character sets into one enormous encoding which gives every possible character a unique numeric code. The advantages to this are consistency and ease of use. The draw back is that using Unicode can result in significantly larger files.
Macintoshes can use a completely different approach.
There are Mac fonts that simple replace standard Latin glyphs with Cyrillic glyphs without changing the underlying encoding. While this is simple approach to using Cyrillic, it limits the usefulness of the resulting document since it can only be read on systems with the correct font. This is a significant problem when writing email or building web pages and generally this solution should not be used for documents that you intend to share. This is not the same as the Apple Standard Cyrillic which is a real Cyrillic encoding. In general we recommend using a Cyrillic encoding, either Apple Standard or KOI8 or Unicode rather than just using a non-encoded Cyrillic font.