Adolescence /ˌæd

peer /pɪə r / /pɪr/ noun [ C ] EQUAL
1. a person who is the same age or has the same social position or the same abilities as other people in a group
Do you think it's true that teenage girls are less self-confident than their male peers?
He wasn't a great scholar, but as a teacher he had few peers (= not as many people had the same ability as him) .
period /ˈpɪə.ri.əd/ /ˈpɪr.i-/ noun [ C ] TIME
1. a length of time
Her work means that she spends long periods away from home.
Unemployment in the first half of 1993 was 2% lower than in the same period the year before.
Fifteen people were killed in/over a period of four days.
The study will be carried out over a six-month period.
2. in school, a division of time in the day when a subject is taught
We have six periods of science a week.
3. a fixed time during the life of a person or in history
Most teenagers go through a rebellious period.
The house was built during the Elizabethan period.
phase /feɪz/ noun [ C ]
1. any stage in a series of events or in a process of development
The project is only in the initial phase as yet, but it's looking quite promising.
We're entering a new phase in international relations.
2. a period of strange or difficult behaviour, especially that a young child or person goes through, that will stop after a while
When I was in my early teens I went through a phase of only ever wearing black.
3. The phases of the moon are the regular changes in its shape as it appears to us on Earth.