A (upper case) or a (lower case), usually referred to in English as A-breve, is a letter used in standard Romanian language and Vietnamese language orthographies. In Romanian, it is used to represent the mid-central unrounded vowel, while in Vietnamese it represents the short a sound. It is the second letter of both the Romanian, Vietnamese, and the pre-1972 Malaysian alphabets, after A.

For A. E. van Vogt's novel, see The World of Null-A.

A, lowercase a, is a grapheme, a Latin A with a macron, is used in several orthographies.

A (minuscule: a) is a letter in the Polish, Kashubian, Lithuanian, Creek, Navajo, Western Apache, Chiricahua, Hocak, Mescalero, Gwich'in, Tutchone, and Elfdalian alphabets. It is formed from the letter a and an ogonek and usually – except for modern Polish – denotes a nasal a sound.

A (named , plural As, A's, as, a's or aes) is the first letter and the first vowel in the ISO basic Latin alphabet. It is similar to the Ancient Greek letter alpha, from which it derives. The upper-case version consists of the two slanting sides of a triangle, crossed in the middle by a horizontal bar. The lower-case version can be written in two forms: the double-storey a and single-storey ɑ. The latter is commonly used in handwriting and fonts based on it, especially fonts intended to be read by children. It is also found in italic type.

(a-grave) is a letter of the Catalan, French, Galician, Italian, Occitan, Portuguese, Scottish Gaelic, Vietnamese, and Welsh languages consisting of the letter A of the ISO basic Latin alphabet and a grave accent. À is also used in Pinyin transliteration. In most languages, it represents the vowel a. This letter is also a letter in Taos.

(a-acute) is a letter of the Czech, Faroese, Hungarian, Icelandic, Irish, Sámi and Slovak languages. This letter also appears in Dutch, Galician, Lakota, Navajo, Occitan, Portuguese, Spanish, Vietnamese, and Welsh as a variant of the letter “a”. It also appears in Blackfoot. It is sometimes confused with à; e.g. "5 apples á $1", which is more commonly written as "5 apples à $1" ("5 apples at 1 dollar each").

(a-circumflex) is a letter of the French, Friulian, Frisian, Inari Sami, Portuguese, Romanian, Turkish, Vietnamese, Walloon, and Welsh alphabets.

Ã/ã (a-tilde) is a letter used in some languages, generally considered a variant of the letter A.

"Ä" and "ä" are both characters that represent either a letter from several extended Latin alphabets, or the letter A with an umlaut mark or diaeresis.

Å (lower case: å) represents various (although often very similar) sounds in several languages. It is considered a separate letter in the Swedish, Danish, Norwegian and Finnish alphabets, as well as in the North Frisian, Walloon, Emiliano-Romagnolo, Chamorro, Istro-Romanian, Lule Sami, Skolt Sami, Southern Sami, and Greenlandic alphabets. Additionally, it is part of the alphabets used for the Alemannic and the Bavarian-Austrian dialects of German.

(A) or (a) may refer to:

• The anarchy symbol, a letter A intersecting through a circle
• An abbreviation for an Islamic honorific such as Alayhi 'l-salat wa'l-Salam

The A* search algorithm is a pathfinding algorithm used in computing.

In computer science, A* (pronounced as "A star") is a computer algorithm that is widely used in pathfinding and graph traversal, the process of plotting an efficiently traversable path between multiple points, called nodes. Noted for its performance and accuracy, it enjoys widespread use. However, in practical travel-routing systems, it is generally outperformed by algorithms which can pre-process the graph to attain better performance, although other work has found A* to be superior to other approaches.

A+ may refer to:

• A+ (blood type)
• A+ (grade), the highest grade achievable in a grading system based on letters of the alphabet
• A+ (programming language), a dialect of APL with aggressive extensions
• A+ (rapper), Andre Levins, an American rapper
• A+ (EP), 2015 EP by Hyuna
• A-Plus (rapper), Adam Carter, an American rapper
• A+ certification, the professional computer technician certification by CompTIA
• Animax Eastern Europe, an Eastern European anime TV channel formerly known as A+
• A-Plus, an American convenience store chain owned & operated by Sunoco
• A-Plus Entertainment, a television station in Pakistan
• A Plus (aplus.com), a social news company based in New York City.

A++ stands for abstraction plus reference plus synthesis which is used as a name for the minimalistic programming language that is built on ARS. ARS is an abstraction from the Lambda Calculus, taking its three basic operations, and giving them a more general meaning, thus providing a foundation for the three major programming paradigms: functional programming, object-oriented programming and imperative programming.

A- or a- may refer to:

A-hyphen

• A- (plane), a U.S. military aircraft prefix
• Privative a, a prefix expressing negation
• Copulative a, a prefix expressing unification

Alpha (uppercase Α, lowercase α; Álpha) is the first letter of the Greek alphabet. In the system of Greek numerals it has a value of 1. It was derived from the Phoenician letter aleph . Letters that arose from alpha include the Latin A and the Cyrillic letter А.

A bell code (sometimes bell character) is a device control code originally sent to ring a small electromechanical bell on tickers and other teleprinters and teletypewriters to alert operators at the other end of the line, often of an incoming message. Though tickers punched the bell codes into their tapes, printers generally do not print a character when the bell code is received. Bell codes are usually represented by the label "BEL". They have been used since 1870 (initially in Baudot code).

A blood type (also called a blood group) is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system. Some of these antigens are also present on the surface of other types of cells of various tissues. Several of these red blood cell surface antigens can stem from one allele (or an alternative version of a gene) and collectively form a blood group system. Blood types are inherited and represent contributions from both parents. A total of 35 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT). The two most important ones are ABO and the RhD antigen; they determine someone's blood type (A, B, AB and O, with +, - or Null denoting RhD status).

A caron or háček (; from Czech háček ) or mäkčeň (; from Slovak mäkčeň or ), also known as a wedge, inverted circumflex, inverted hat, is a diacritic ( ˇ ) placed over certain letters to indicate present or historical palatalization, iotation, or postalveolar pronunciation in the orthography of some Baltic, Slavic, Finnic, Samic, Berber and other languages. The caron also indicates the third tone (falling and then rising) in the Pinyin romanization of Mandarin Chinese.

"Dance (Ass)", often stylized "Dance (A$$)", is a song by American rapper Big Sean, released as the third single from his debut studio album, Finally Famous (2011). It was added to urban radio formats on September 20, 2011 as the album's third official single. The official remix of the song features Nicki Minaj and was made available for free download on her website.

In computing, drive letter assignment is the process of assigning alphabetical identifiers to volumes. Unlike the concept of UNIX mount points, where volumes are named and located arbitrarily in a single hierarchical namespace, drive letter assignment allows multiple highest-level namespaces. Drive letter assignment is thus a process of using letters to name the roots of the "forest" representing the file system; each volume holds an independent "tree" (or, for non-hierarchical file systems, an independent list of files).

In computer science, a static library or statically-linked library is a set of routines, external functions and variables which are resolved in a caller at compile-time and copied into a target application by a compiler, linker, or binder, producing an object file and a stand-alone executable. This executable and the process of compiling it are both known as a static build of the program. Historically, libraries could only be static. Static libraries are either merged with other static libraries and object files during building/linking to form a single executable, or they may be loaded at run-time into the address space of the loaded executable at a static memory offset determined at compile-time/link-time.