The word Hajj, linguistically, means heading to a place for the sake of visiting; in Islamic terminology, it implies heading to Makkah to observe the rituals of pilgrimage.
Hajj is obligated by Allah upon every Muslim, male and female, who is physically and financially capable. It is obligatory only once during the lifetime of a Muslim. Allah Almighty Says (what means): {…And [due] toAllah from the people is a pilgrimage to the House – for whoever is able to find thereto a way….} [Quran 3:97]
The Prophet said: “Islam is built upon five (pillars): the testimony that none has the right to be worshipped except Allah and Muhammad is the Messenger of Allah, the establishment of the prayer, paying Zakat, Hajj to the House (i.e. Ka’bah,) and fasting in Ramadan.” [Al-Bukhari and Muslim]
The Prophet also said: “Hajj is mandated once, so whoever does it more (than that), then it is supererogatory.” [Abu Daawood and Ahmad]