also: かっかい
noun
each time; every time; each installment
Used to refer to each occurrence or episode of a recurring event, series, or broadcast.
このドラマは各回が独立したストーリーになっている。
Each episode of this drama is a self-contained story.
各回の講義で新しいテーマ
We cover a new topic in each lecture session.
毎回 means 'every time' without exception, while 各回 emphasizes each individual occurrence, often in a series.
Compound of 各 (each) and 回 (time/occurrence). The reading かっかい is a euphonic change from かくかい.