Æ
Æ, æ is a vowel and a letter used in the Icelandic, Danish and Norwegian alphabets. It was also used in Old English, and in medieval and early modern Latin.
The origin of the letter is a ligature for ae that has become a letter in itself. But in modern Danish, Icelandic and Norwegian, the letter is a unique vowel, not a diphthong, umlaut or ligature. In German and Swedish, the letter Ä (A with a diaeresis) is the equivalent.
In Old English, the ligature was used to denote a sound intermediate between those of A and E (IPA [æ]). In this context, the name of the letter is Æsc (Ash), after the name of the corresponding letter in the Futharc.
In Latin, the combination denotes a diphthong that had much the same value as the ai in English aisle both in native words (spelled as ai before the 2nd century BC) and in borrowings from Greek words having the diphthong ai (αι). Both classical and modern practice is to write the letters separately, but the ligature was used in medieval and early modern writings, in part because æ was reduced to a simple long vowel in late Latin.
The symbol æ is also used in the International Phonetic Alphabet to denote the sound of the Old English letter, an unrounded, semi-open front vowel, similar to short a sound of cat in many dialects of modern English.
For computers, when using the Latin-1 or Unicode sets, the codes for 'Æ' and 'æ' are respectively 198 and 230, or C6 and E6 in hexadecimal. In HTML, you can also use the HTML character entity references Æand æ.