Definition of labour:

Series of events that take place in the genital organs in an effort to expel the viable products of conception out of the womb through the vagina into the outer world is called labour.

Means a number of events such as engagement, descent, flexion, internal rotation of head, crowning, extension, restitution, delivery of the shoulder and trunk , that take place in the female genital organ such as uterus, pelvis, and vagina to expel the fetus from mother womb to outer world is called labour.