希腊字母的第六个字母
The sixth letter of the Greek alphabet.
代数学计算的普遍原理，其中通常为字母表中字母的符号，其代表数字或一组特定数字中的几个数字，它们通过对组中全部数字都适合的运算法则相联系
A generalization of arithmetic in which symbols, usually letters of the alphabet, represent numbers or members of a specified set of numbers and are related by operations that hold for all numbers in the set.
