A classmate or someone who graduated in the same class/cohort — people who were in the same year or intake.
大学の同期生と毎年同窓会を開いている。
I hold a reunion every year with my university classmates.
同期生の多くは東京で働いている。
Many of my cohort are working in Tokyo.
入社した当時の同期生とは今でも連絡を取っている。
I still keep in touch with the people who joined the company at the same time as me.
In sumo, wrestlers who began their professional careers in the same tournament — i.e., those who debuted together as part of the same intake.
彼は有名な横綱と同期生だったが、怪我で引退した。
He was in the same intake as a famous yokozuna, but retired due to injury.
同期生同士の対戦は、観客にとって特別な意味を持つことが多い。
Matches between same-intake wrestlers often carry special meaning for spectators.