What is the difference between stockless purchasing and just in time delivery?

My understanding of the two concepts is that they are very similar, if not the same, and the definitions I have found online have not persuaded me otherwise. I am missing something? Is there a fundamental difference between the two concepts that anyone can share with me? The online course materials for the CIPS Diploma in Procurement & Supply includes reference to both concepts, the course book only refers to JIT, and no definition given yet for stockless purchasing to differentiate it from JIT.