Descent refers to the downward movement of the fetus through the maternal pelvis during labor. This process is crucial as it advances the fetus towards the birth canal, enabling progression of labor. It occurs due to uterine contractions and maternal pushing efforts. Without descent, the fetus cannot properly engage in the pelvis, making vaginal delivery impossible. Other mechanisms like rotation or cervical dilation are distinct processes; descent specifically ensures the fetus moves through the pelvic inlet and midpelvis.

Reference: Williams Obstetrics, Cunningham et al, 25th Edition.