is the symbol for the atomic mass unit and 'U' is the symbol for one Enzyme unit. In IPA, the close back rounded vowel is represented by the lower case ⟨u⟩. U is also the source of the mathematical symbol ∪, representing a union. It is used mainly for Venn diagrams and geometry. It is used as for micro- in metric measurements as a replacement for the Greek letter μ (mu), of which it is a graphic approximation when that Greek letter is not available, as in "um" for μm (micrometer). Some universities, such as the University of Miami and the University of Utah, are locally known as "The U". U (or sometimes RU) is a standard height unit of measure in rack units, with each U equal to . U is also used the letter in the coat of arms/flag of the Ustaše. U is a honorific in Burmese. Related characters Ancestors, descendants and siblings 𐤅: Semitic letter Waw, from which the following symbols originally derive υ : Greek letter Upsilon, from which U derives V v : Latin letter V, descended from U W w : Latin letter W, descended frm V/U Y y : Latin letter Y, also descended from Upsilon У у : Cyrillic letter U, which also derives from Upsilon Ү ү : Cyrillic letter Ue Ϝ ϝ : Greek letter Digamma F f : Latin letter F, derived from Digamma IPA-specific symbols related to U: Uralic Phonetic Alphabet-specific symbols related to U: Teuthonista phonetic transcription-specific symbols related to U: ᶸ : Modifier letter small capital u is used for phonetic transcription Ꞿ ꞿ : Glottal U, used in the transliteration of Ugaritic U with diacritics: Ŭ ŭ Ʉ ʉ ᵾ ᶶ Ꞹ ꞹ Ụ ụ Ü ü Ǜ ǜ Ǘ ǘ Ǚ ǚ Ǖ ǖ Ṳ ṳ Ú ú Ù ù Û û Ṷ ṷ Ǔ ǔ Ȗ ȗ Ű ű Ŭ ŭ Ư ư Ứ ứ Ừ ừ Ử ử Ự ự Ữ Ữ Ủ ủ Ū ū Ū̀ ū̀ Ū́ ū́ Ṻ ṻ Ū̃ ū̃ Ũ ũ Ṹ ṹ Ṵ ṵ ᶙ Ų ų Ų́ ų́ Ų̃ ų̃ Ȕ ȕ Ů ů and are used in the Mazahua language and feature a bar diacritic Ligatures and abbreviations ∪ : Union ∩ : Intersection, an upside-down upper case "U" Computing codes 1 Other representations References External links Vowel letters ISO basic Latin letters