It means the process by which the baby is born. Labor, delivery or birth requires:
1) Dilation of the cervical canal to accommodate passage of the foetus to outside.
2) Contraction of the uterine myometrium to expel the fetus.
Weak contraction of uterine muscle occur infrequently throughout the third trimester. As parturition approaches these contraction become stronger and regular and more frequent and know as Braxton-Hickes contraction.
Labor is begin when uterine contraction start to occur once every 10-15 minutes. Uterine contraction begin in the upper portion of uterus and more down toward the cervix so push the fetus towards the cervix and lead to dilate of the cervix to reach about 10 cm.