As I was going through the book 'The Design and Engineering of Curiosity' by Emily Lakdawalla, I stumbled on these two words. Are they hot and cold section of thermocouple? What actually they do?
The following lines are from that book:
A radioisotope thermoelectric generator converts heat into electricity with no moving parts by taking advantage of the thermoelectric effect. Holding two different electrically conductive materials at different temperatures and joining them in a closed circuit generates current. A pair of conductive materials joined in this way is called a thermocouple. A thermocouple has a “hot shoe” and a “cold shoe.” In Curiosity’s MMRTG, the decaying plutonium heats the hot shoes of the thermocouples. External fins splaying out into the Martian air chill the cold shoes.
Here a the link to Section 4.2.1 "How the MMRTG Works" in Lakdawalla's book.