When Madame L first saw this word on a university's online catalog, she thought it was a joke or a misprint.
It isn't. It is a joint degree program common in many universities in which doctoral students from one university can participate with adviser(s) at another university, even when the two universities are in different countries.
One university website explains it like this: "The aim is to establish deep, continuing relationships with international research universities through the joint research candidate supervision."
Origin of the word: It comes from the French, where it can mean "joint guardianship" or "teaching participated in by several persons."