A juz' is one of thirty parts of roughly equal length into which the Qur'an

Qur'an

The Quran , also transliterated Qur'an, Koran, Alcoran, Qur’ān, Coran, Kuran, and al-Qur’ān, is the central religious text of Islam, which Muslims consider the verbatim word of God . It is regarded widely as the finest piece of literature in the Arabic language...

 is sometimes divided. This division facilitates recitation of the Qur'an in a month, especially during Ramadan

Ramadan

Ramadan is the ninth month of the Islamic calendar, which lasts 29 or 30 days. It is the Islamic month of fasting, in which participating Muslims refrain from eating, drinking, smoking and sex during daylight hours and is intended to teach Muslims about patience, spirituality, humility and...

 when the entire Qur'an is recited in the Tarawih

Tarawih

Tarawih refers to extra congregational prayers performed by Muslims at night in the Islamic month of Ramadan. They are not compulsory; however, many Muslims pray these prayers in the night during Ramadan...

 salat

Salat

Salah is the practice of formal prayer in Islam. Its importance for Muslims is indicated by its status as one of the Five Pillars of Sunni Islam, of the Ten Practices of the Religion of Twelver Islam and of the 7 pillars of Musta'lī Ismailis...

; reciting approximately one juz' a night. A juz' is further divided into two ahzab (groups), and each hizb (group) is in turn subdivided into four quarters. The most commonly referred and memorized juz' is "juz' Amma'," which is the 30th juz' and contains Surahs 78 through 114, most of the shortest sura

Sura

A sura is a division of the Qur'an, often referred to as a chapter. The term chapter is sometimes avoided, as the suras are of unequal length; the shortest sura has only three ayat while the longest contains 286 ayat...

s in the Qur'an. 'Amma is generally taught first to children. Juz Amma is named after the 1st word of the 1st sura (i.e. sura 78) in that juz. Muslims from South Asia

South Asia

South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...

 also refer to a juz' as a para (paara) http://www.ilaam.net/PDF/QuranOrg.pdf.

Juz	Hizb	Sura Sura A sura is a division of the Qur'an, often referred to as a chapter. The term chapter is sometimes avoided, as the suras are of unequal length; the shortest sura has only three ayat while the longest contains 286 ayat... s
1	1	(1:1) - (2:74)
	2	(2:75) - (2:141)
2	3	(2:142) - (2:202)
	4	(2:203) - (2:252)
3	5	(2:253) - (3:14)
	6	(3:15) - (3:92)
4	7	(3:93) - (3:170)
	8	(3:171) - (4:23)
5	9	(4:24) - (4:87)
	10	(4:88) - (4:147)
6	11	(4:148) - (5:26)
	12	(5:27) - (5:81)
7	13	(5:82) - (6:35)
	14	(6:36) - (6:110)
8	15	(6:111) - (6:165)
	16	(7:1) - (7:87)
9	17	(7:88) - (7:170)
	18	(7:171) - (8:40)
10	19	(8:41) - (9:33)
	20	(9:34) - (9:92)
11	21	(9:93) - (10:25)
	22	(10:26) - (11:5)
12	23	(11:6) - (11:83)
	24	(11:84) - (12:52)
13	25	(12:53) - (13:18)
	26	(13:19) - (14:52)
14	27	(15:1) - (16:50)
	28	(16:51) - (16:128)
15	29	(17:1) - (17:98)
	30	(17:99) - (18:74)
16	31	(18:75) - (19:98)
	32	(20:1) - (20:135)
17	33	(21:1) - (21:112)
	34	(22:1) - (22:78)
18	35	(23:1) - (24:20)
	36	(24:21) - (25:20)
19	37	(25:21) - (26:110)
	38	(26:111) - (27:55)
20	39	(27:56) - (28:50)
	40	(28:51) - (29:45)
21	41	(29:46) - (31:21)
	42	(31:22) - (33:30)
22	43	(33:31) - (34:23)
	44	(34:24) - (36:27)
23	45	(36:28) - (37:144)
	46	(37:145) - (39:31)
24	47	(39:32) - (40:40)
	48	(40:41) - (41:46)
25	49	(41:47) - (43:23)
	50	(43:24) - (45:37)
26	51	(46:1) - (48:17)
	52	(48:18) - (51:30)
27	53	(51:31) - (54:55)
	54	(55:1) - (57:29)
28	55	(58:1) - (61:14)
	56	(62:1) - (66:12)
29	57	(67:1) - (71:28)
	58	(72:1) - (77:50)
30	59	(78:1) - (86:17)
	60	(87:1) - (114:6)