Y (named wye //, plural wyes) is the twenty-fifth letter in the ISO basic Latin alphabet (next to last letter) and represents either a vowel or a consonant in English.
In Latin, Y was named Y Graeca "Greek Y". This was pronounced as I Graeca "Greek I", since the classical Greek sound /y/, similar to modern German ü or French u, was not a native sound for Latin speakers, and the letter was initially only used to spell foreign words. In Romance languages, this history has led to the standard modern name of the letter: In Spanish, Y is called i griega, in Galician i grego, in Catalan i grega, in French and Romanian i grec - all meaning "Greek i". The names igrek in Polish and i gờ-rét in Vietnamese are both phonetic borrowings of the French name. In Dutch, both Griekse ij and i-grec are used. The original Greek name upsilon has also been adapted into several modern languages; in German, for example, it is called Ypsilon, and in Italian the name is ípsilon or ípsilo. In Portuguese, both names are used (ípsilon and i grego). 
Old English borrowed Latin Y to write the native Old English sound /y/ (previously written with the rune yr ᚣ). The name of the letter may be related to 'ui' (or 'vi') in various medieval languages; in Middle English it was 'wi' /wiː/, which through the Great Vowel Shift became the Modern English 'wy' /waɪ/.