It means any obligatory act on which the validity of Hajj depends and which is redeemed by offering a sacrifice.

According to this school: the obligatory act may be represented as the Essential [Al-Rukn], and it includes the Requisite [Al-Shart].

The Four Obligatory Acts of Hajj:

1. Ihram

2. Standing by `Arafah

3. Ifadah Circumambulation

4. Sa`i between Safa and Marwah

There is agreement among Juristic Schools on the obligatory and necessary rituals of Hajj.