pi
/paɪ; paɪ/ n
1 the sixteenth letter of the Greek alphabet (, ), represented in English spelling by `p' 希腊字母表的第十六个字母（）, 英语拼写中用 p.
2 (geometry 几) symbol () representing the ratio of the circumference of a circle to its diameter (ie 3.14159) 圆周率（即3.14159）.