A confirm obligation on everyone (a man-made term)
Its neither in the Holy Quran nor in Ahadith but people coined this term, see for example;
ثمراتها و علاجها هو علم الآخرة و هو فرض عين فى فتوى علماء الآخرة
Its fruits and cure lie in the knowledge of the Hereafter, and this is an individual obligation according to the fatwas of scholars related to the Hereafter (religion).[1]
[1] شرح أصول الكافي (صدرا)، ج2، ص: 22