What is the origin of the phrase "How many angels can dance on a pin?"?

Answer 1

That was an argument among medieval clerics concerning the nature of Angels. Some argued that angels in their natural form were spirits without physical form and therefore any number of angels could occupy even the smallest space. Others argued that angels had a physical body and were confined to a physical more or less like humans.

Answer 2

means that angels are not physical so you can have thousands of angels on a pin dancing