The orthography of a language specifies the correct way of using a specific writing system to write the language. (Where more than one writing system is used for a language, for example for Kurdish, there can be more than one orthography.) Orthography is derived from Greek ὀρθός orthós ("correct") and γράφειν gráphein ("to write"). Orthography is distinct from typography.
Orthography describes or defines the set of symbols (graphemes and diacritics) used, and the rules about how to write these symbols. Depending on the nature of the writing system, the rules may include punctuation, spelling and capitalization.
An orthography may be described as "efficient" if it has one grapheme per phoneme (distinctive speech sound) and vice versa. An orthography may also have varying degrees of efficiency for reading or writing. For example, diverse letter, digraph, and diacritic shapes contribute to diverse word shapes, which aid fluent reading, while heavy use of apostrophes or diacritics makes writing slow, and the use of symbols not found on standard keyboards makes computer or cell phone input awkward.
See main article: Phonemic orthography. A phonemic orthography is an orthography that has a dedicated symbol or sequence of symbols for each phoneme (distinctive speech sound) and vice versa, that is, graphemes and phonemes are bijective functions of one another. Spanish and Italian are very close to being phonemic, and English is among the least.
A morpho-phonemic orthography considers not only what is phonemic, as above, but also the underlying structure of the words. For example, in English, and are distinct phonemes, so in a phonemic orthography the plurals of cat and dog would be cats and dogz. However, English orthography recognizes that the sound in cats and the sound in dogs are the same element (archiphoneme), automatically pronounced differently depending on its environment, and therefore writes them the same despite their differing pronunciation. German and Russian are morpho-phonemic in this sense, whereas Turkish is purely phonemic. Korean hangul has changed over the centuries from a highly phonemic to a largely morpho-phonemic orthography, and there are moves in Turkey to make that script more morpho-phonemic as well.
A "defective orthography" is one in which there is not a one-to-one correspondence between the letters and the phonemes in the language, such as those of English or Arabic. Most languages of western Europe (which are written with the Latin alphabet), as well as the modern Greek language (written with the Greek alphabet), have defective scripts. In some of these, there are sounds with more than one possible spelling, usually for etymological or morpho-phonemic reasons (like in English, which can be written with "j", "g", "dj", "dg", or "ge"). In other cases, the letters in the alphabet are not enough to write all phonemes. The remaining ones must then be represented by using such devices as diacritics, digraphs that reuse letters with different values (like "th" in English, whose sound value is normally not), or simply inferred from the context (for example the short vowels in abjads like the Arabic and the Hebrew alphabet, which are normally left unwritten).
Another term to describe this characteristic is "deep orthography". (Note that the term "defective orthography" should not indicate that the writing system is flawed; some defects, such as the aforementioned absence of short vowels in abjads for Semitic languages, serve the languages better than a supposedly "perfect" orthography would.) Deep orthographies are writing systems that do not have a full correspondence between the spoken phoneme and the written grapheme (as listed above). Shallow orthographies, however, have a one-to-one relationship between graphemes and phonemes. The phonetic writing of Japanese (ex. hiragana) is an example of shallow orthography.
Complex orthographies often combine different types of scripts and/or utilize many different complex punctuation rules. Some widely accepted examples of languages with complex orthographies include Thai, Japanese, and Khmer.