IIRC, lightening is when an unborn baby descends into the pelvic cavity, occurring toward the end of pregnancy, changing the contour of the abdomen and making breathing easier by lessening pressure under the diaphragm. The mother experiences a lightening of her breathing.
According to the Oxford Dictionary...”a drop in the level of the uterus during the last weeks of pregnancy as the head of the fetus engages in the pelvis”
So, yep.