The literal meaning of the word Hajj is "heading to a place for the sake of visiting". In Islamic terminology, Hajj is a pilgrimage made to Kaaba, the "House of Allah", in the sacred city of Mecca in Saudi Arabia. The rites of Hajj are performed over five or six days, beginning on the eighth and ending on the thirteenth day of Dhu al-Hijjah, the last month of the Islamic calendar. It is one of the five pillars of Islam, alongside Shahadah, Salat, Zakat and Sawm. The Hajj is the second largest annual gathering of Muslims in the world, after the Arba'een Pilgrimage in Karbala, Iraq. The state of being physically and financially capable of performing the Hajj is called istita'ah, and a Muslim who fulfills this condition is called a mustati. The Hajj is a demonstration of the solidarity of the Muslim people, and their submission to God (Allah). The word Hajj means "to attend a journey", which connotes both the outward act of a journey and the inward act of intentions.
The pilgrimage occurs from the 8th to 12th (or in some cases 13th) of Dhu al-Hijjah, the last month of the Islamic calendar. Because the Islamic calendar is lunar and the Islamic year is about eleven days shorter than the Gregorian year, the Gregorian date of Hajj changes from year to year. Ihram is the name given to the special spiritual state in which pilgrims wear two white sheets of seamless cloth and abstain from certain actions.
The Hajj (sometimes spelt Hadj, Hadji or Haj also in English) is associated with the life of Islamic prophetMuhammad from the 7th century AD, but the ritual of pilgrimage to Mecca is considered by Muslims to stretch back thousands of years to the time of Abraham. During Hajj, pilgrims join processions of millions of people, who simultaneously converge on Mecca for the week of the Hajj, and perform a series of rituals: each person walks counter-clockwise seven times around the Kaaba (the cube-shaped building and the direction of prayer for the Muslims), trots (walks briskly) back and forth between the hills of Safa and Marwah seven times, then drinks from the Zamzam Well, goes to the plains of Mount Arafat to stand in vigil, spends a night in the plain of Muzdalifa, and performs symbolic stoning of the devil by throwing stones at three pillars. After the sacrifice of their animal, the Pilgrims then are required to shave their head. Then they celebrate the three-day global festival of Eid al-Adha.
Muslims may also undertake an Umrah (Arabic: عُمرَة), or "lesser pilgrimage" to Mecca at other times of the year. But this is not a substitute for the Hajj and Muslims are still obligated to perform the Hajj at some other point in their lifetime if they have the means to do so. 
In 2017, the number of pilgrims coming from outside the Saudi Arabia to perform Hajj was officially reported as 1,752,014 and 600,108 Saudi Arabian residents bringing the total number of pilgrims to 2,352,122.
The word in Arabic: حج [ħædʒ, ħæɡ] similar to the Hebrew: חג ḥag[χaɡ], which means "holiday", from the triliteral ח-ג-ג. The meaning of the verb is "to circle, to go around".Judaism uses circumambulation in the Hakafot ritual during Hoshanah Rabbah at the end of the Festival of Sukkot and on Simchat Torah; traditionally, Jewish brides circumambulate their grooms during the wedding ceremony under the chuppah. From this custom, the root was borrowed for the familiar meaning of holiday, celebration and festivity. In the Temple, every festival would bring a sacrificial feast. Similarly in Islam, the person who commits the Hajj to Mecca has to circle around the Kaaba and to offer sacrifices.