Jean-Jacques Rousseau
In the words of Jean-Jacques Rousseau,
The general will is different from the will of all; the general will considered the common interest, while the will of all considered the private interest, a sum of particular wills; the general will is infallible and the will of all may be fallible; the social conditions that could fulfil the expression the general will.
People should submit their will to the general will which cannot be wrong and whoever refused would be subject to compulsion, so to express the general will is to express every man's common will.
General will is what the body politic (community of citizens) would unanimously do if they were selecting general laws and were choosing/voting with full information, good reasoning, unclouded judgment,(bias and emotion can cloud judgment) public spirit, and attempting to discern the common good.