The meaning of Al-Ijmaa’ in accordance to the Istilaah of the Usooliyeen:
It is the agreement upon the Hukm of a reality from amongst the realities in respect to it being a Hukm Shar’iy after the passing of the Messenger of Allah (saw).
The Importance and Significance of Al-Ijmaa’ within the Ahkaam Ash-Shar’iyah
1 – Al-Ijmaa’ is the third Daleel after the Qur’aan and the Sunnah because it based upon a Daleel Shar’iy even though that Daleel did not reach us (directly) but rather only the Hukm deduced from it has reached us.
2 – The ‘Ulamaa of the Muslims have made Ijmaa’ (held a consensus)
upon Al-Ijmaa’ representing a Hujjah (proof and evidence) even if they have differed in respect to those who are the people of Ijmaa’ and whose agreement indicates and guides to the convening of AlIjmaa’ (a consensus).
3 – The Fuqahaa dedicated special attention and care to identify and acquire knowledge of the areas and contexts of Ijmaa’ amongst the Sahaabah (rah) so as to follow them within them. This is whilst every Mujtahid dedicated special care and attention do not go outside of that which the Sahaabah (rah) had agreed and held an Ijmaa’ upon.
4 - The Hukm that has been established by Al-Ijmaa’ is not abrogated because it came after the death of the Messenger of Allah (saw) and after the Wahi had ceased to descend.
5 – The Sahaabah (rah) have transmitted the Usool ud-Deen to us by their Ijmaa’ as they have transmitted to us the Qur’aan Al-Kareem and the Sunnah An-Nabawiyah which indicates and guides to the importance and significance of Al-Ijmaa’.