A more thorough explanation:

ignis judicium

Ignis judicium is a historical practice where a person's guilt or innocence was determined by subjecting them to a trial by fire. This was a form of ordeal by fire.

One example of ignis judicium is the trial by fire of Saint Lawrence, a Christian martyr who was burned alive on a gridiron. Another example is the trial by fire of Joan of Arc, who was burned at the stake after being accused of heresy.

These examples illustrate how ignis judicium was used as a means of determining guilt or innocence. In both cases, the accused were subjected to the ordeal of fire, and their fate was believed to be determined by divine intervention. If they survived the flames, they were considered innocent, but if they perished, they were deemed guilty.