Small units of the glorious Qur'an. In most cases, every verse is one sentence. But sometimes, there are verses which are comprised of some sentences and make a paragraph (such as Ayat al-Kursi or the verse of Nur). Even, there are verses which are about some paragraphs such as the verse of Dayn (also called Tadayun and Mudayana) which are the lengthiest verse of the Qur'an and in 'Uthman Taha (Mushaf Madina) print, it takes a full 15-line page.
Sometimes, a verse is shorter than a sentence and even as short as one word such as (55:64) or even shorter than that such as most Huruf Muqatta'a [disconnected letters], or Fawatih al-Suwar [beginning of Surahs] such as طه [Taha], یس [Yasin], الم [Alif, Lam, Mim]. Interpreting a verse is Tawqifi [absolute and definite] and only made by religion; since, some beginnings of surahs have been regarded as one verse such as المص [Alif, Lam, Mim, Sad] (7:1), but they have not considered another similar beginning as one verse such as المر [Alif, Lam, Mim, Ra] (13:1); or حمعسق [Ham, Mim, 'Ayn, Sin, Qaf] (41:1) (= حم. عسق) have been regarded as two verses. But, کهیعص [Kaf, Ha, Ya, 'ayn, Sad] (19:1) has been considered as one verse.
The word Ayah and its plural which is Ayat mean these sentences or phrases in the Qur'an. The surah with most verses in the glorious Qur'an is the Sura Baqara [the Cow] with 286 verses and the Surah with least number of verses is the Surah al-Kawthar with 3 verses. There are different opinions about the number of verses in the Qur'an. The most authentic opinion is Abu 'Abd al-Rahman b. Habib Sullami's narration from Imam Ali (a) quoted in Imam Shatibi's Nazimat al-zuhar in which the number of verses of the Qur'an is mentioned as 6236.
Larger units in the Qur'an are Surahs. The word "Surah" means "cut or disconnected" and it refers to an independent group of verses in the Qur'an which have a beginning and an end; and it is also said that it is adopted from the phrase "Suwar al-Madina" [meaning "walls of the city"]. The word Surah means the same in the Qur'an. Also, its plural form "Suwar" has been used in the Qur'an. The noble Qur'an has 114 Surahs which are somehow ordered according to their length. The longest surah of the Qur'an is Baqarah (having 286 verses which takes 48 pages of 'Uthman Taha [Mushaf Madina] print) and the shortest surah is Kawthar (which has 3 verses).
There are different views on whether the order and sequence of the surahs of the Qur'an which begin with Fatihat al-Kitab and end of them is the Surah Nas is absolute and definite or depending on judgment (the judgment of the Companions) and it depends on compilers' opinions and views. Some have said that it is definite according to the order and instructions of the Prophet (s) and revelation.
Some others have said that it depends on judgment of the compiler of Mushaf 'Uthmani [the 'Uthmani compiled version], because the Prophet (s) compiled the Qur'an but it was not organized at his time. Also, some other have said that it is a partly definite and partly depending on judgment which is more acceptable. The name and description of 114 surahs of the Qur'an are mentioned in most historical references of the Qur'an (including Ramyar's Tarikh-e Qur'an, p. 583) as well as the statistics of the words and letters which are mentioned in statistical references of the words of the glorious Qur'an written by Dr. Mahmoud Rohani and also at the end of every new printing of the Qur'an.