The notion of Z-variance is only applicable to the "CJKV scripts"—Chinese, Japanese, Korean and Vietnamese—and is a subtopic of Han unification.
The Unicode philosophy of code point allocation for CJK languages is organized along three "axes."
The X-axis represents differences in semantics; for example, the Latin capital A (U+0041 A) and the Greek capital alpha (U+0391 Α) are represented by two distinct code points in Unicode, and might be termed "X-variants" (though this term is not common).
For example, in an Internet Draft (of RFC 3743) dated 2002,[2] one finds bù "no" (U+4E0D 不) and (U+F967 不︀) described as "font variants," the term "Z-variant" being apparently reserved for interlanguage pairs such as the Mandarin Chinese tù "rabbit" (U+5154 兔) and the Japanese to "rabbit" (U+514E 兎).
However, the Unicode Consortium's Unihan database[3][failed verification – see discussion] treats both pairs as Z-variants.