It comes from the word catre and has an aceptivity as a prostitute (who works in a cot), although in lunfardo it was always a "bed", in the most general sense.
It means bunk bed, cot, makeshift bed. Woman who sells cotres. It can also mean street woman, prostitute, meretriz.
It is a makeshift bed used to sleep outside on the night of heat in houses where there was no air conditioning...
catrera 40 River Plate lunfardo Word;Argentina, Uruguay ) that refers to the bed.