Ø is a letter used in the Danish, Norwegian, Faroese, and Southern Sámi languages. It is mostly used as to represent the mid front rounded vowels, such as and, except for Southern Sámi where it is used as an diphthong. The name of this letter is the same as the sound it represents. The symbol "ø" is called "slashed O" or "o with a stroke." It is a letter used in several languages, including Danish and Norwegian, where it represents a vowel sound. In the International Phonetic Alphabet (IPA), it is used to represent a close-mid front rounded vowel. The "ø" is also used in various mathematical and technical contexts, often denoting diameter. In linguistics and phonetics, it serves to represent specific vowel sounds in the transcription of words. It was actually mainly a political decision back in the mid-1500’s that made the usage of Ö instead of Ø definite. Before 1523 all of Scandinavia—plus Finland, Iceland and the Faroe Islands—belonged to the Kalmar Union, which for most of its existence was headed by Denmark. The language wasn’t seen as three different ones like today either, instead it was called “Danish Tongue” and even though there was no written standard, many in Sweden and Norway wrote in a more Danish-like way than they spoke. During the Late Middle Ages, the letters Ø and Ö were pretty much in free variation, as were Æ and Ä, but by the early 16th century they had started gravitating towards the former variant of each pair, which is why those letters are the ones used in today’s Danish, Norwegian and Faroese. (Icelandic uses Æ and Ö for very good reasons that I will leave to people with a better grasp of that language’s history.) Enter a nobleman by the name of Gustav, from a house that was later to be known as Vasa. When he was a young man, Sweden was pretty much in constant turmoil; there were always some noblemen rebelling against the Crown, and this led to several old established houses losing their power or even disappearing altogether, which upset their friends so there was a new rebellion, and on and on it went. So, the Danish king—who had a very good claim on the Swedish throne, having been elected the heir to it in 1497 and all—decided to capture a few young Swedish nobles to persuade them to not fight but instead join his side and make peace, and Gustav was one of them, The problem was that he instead developed a deep hatred for Danes and everything Danish because of this captivity, so later when he had been set free and he had lost his father in the Stockholm Bloodbath, he decided to start a rebellion of his own with the goal of making himself King of Sweden and break away from the Kalmar Union once and for all, and he succeeded. Three years after he had been crowned King, he ordered a translation of the New Testament to be made, and since the Bible was pretty much the only book that was guaranteed to be read by everyone who could, it had a tremendous impact on the language, at least in its written form. And still hating everything Danish, King Gustav gave very firm instructions that it had to be truly Swedish and not this Danish-like version that had previously been so common. So, it all boils down to the fact that Danish mostly used Æ and Ø, so Swedish was to use Ä and Ö, and still does to this day. That and it was cheaper and easier to import printing presses and types from what is now Germany wholesale—and just add Åå—instead of having to switch out Ää and Öö for Ææ and Øø. ø is read as phi ø means null set in sets and relations ø means flux in electric and magnetic physics. ø can also be taken as an angle variable in trigonometry. Usually not allowed in website URLs unless the users language is set to a scandinavian setting...