DEFINITION. “In condensed matter physics, a Cooper pair or BCS pair (Bardeen–Cooper–Schrieffer pair) is a pair of electrons (or other fermions) bound together at low temperatures in a certain manner.”
https://en.m.wikipedia.org/wiki/Cooper_pair#:~:text=In%20condensed%20matter%20physics%2C%20a,by%20American%20physicist%20Leon%20Cooper