The romanization of Arabic is the systematic rendering of written and spoken Arabic in the Latin script. Romanized Arabic is used for various purposes, among them transcription of names and titles, cataloging Arabic language works, language education when used instead of or alongside the Arabic script, and representation of the language in scientific publications by linguists. These formal systems, which often make use of diacritics and non-standard Latin characters and are used in academic settings or for the benefit of non-speakers, contrast with informal means of written communication used by speakers such as the Latin-based Arabic chat alphabet.
Google Ngrams chart showing the changing English romanization of the Arabic short vowels (ـَ, ـِ and ـُ) between the 19th and 20th centuries, using مُسْلِم (Muslim) and مُحَمَّد (Muhammad) as examples.
LEBNAAN in proposed Said Akl alphabet (issue #686)
A diacritic is a glyph added to a letter or to a basic glyph. The term derives from the Ancient Greek διακριτικός, from διακρίνω. The word diacritic is a noun, though it is sometimes used in an attributive sense, whereas diacritical is only an adjective. Some diacritics, such as the acute ⟨á⟩, grave ⟨à⟩, and circumflex ⟨â⟩, are often called accents. Diacritics may appear above or below a letter or in some other position such as within the letter or between two letters.
Hangul, the Korean alphabet
German keyboard with umlaut letters
Blackboard used in class at Harvard shows students' efforts at placing the ü and acute accent diacritic used in Spanish orthography.