Adipocere, also known by the terms such as, grave wax and saponified flesh (which create the phenomenon termed as soap mummies) is mostly met with by forensic medical experts, hence its other name of mortuary fat. It’s a greyish-white or yellow waxy substance that forms from the fat of certain parts of dead bodies, especially when fatty tissue are allowed to decompose in an alkaline and wet environment with limited oxygen. Anaerobic bacteria digest fats of the dead body and thereby converting them into a waxy solid. The changes occur quite quickly and can accompany a form of natural mummification.
It’s known to occur in ancient bog bodies and in those preserved in ice, such as the Alpine man Ötzi. It’s also encountered sometimes by archaeologists investigating relatively modern sites containing burials; an example was the difficult and harrowing excavation in the crypt of Christ Church Cathedral in Spitalfields, London, in the early 1980s.
The word derives, via French, in which language the word was first employed in the late eighteenth century, from the Latin adipis, “fat” (as in adipose tissue), and cera, “wax”.