Final answer:
The active labor phase is when the cervix thins and dilates to about 10 cm, and true labor contractions become more frequent and powerful.
Step-by-step explanation:
The active labor phase is a stage during childbirth where the cervix thins and dilates to about 10 cm. True labor contractions, which are regular and do not abate with hydration or rest, become more frequent and powerful with time. This phase is essential for the baby and placenta to be expelled during birth.
An example of active labor is when a woman experiences strong and regular contractions every few minutes, and the cervix progressively opens up to allow the baby to pass through the birth canal.