die Wiederholung
repetition
The repeated performance of an action or the repeated occurrence of an event.
Die Wiederholung dieser Übung hilft, die Muskeln zu stärken.
The repetition of this exercise helps strengthen the muscles.

repetition / rerun / review
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repetition
The repeated performance of an action or the repeated occurrence of an event.
Die Wiederholung dieser Übung hilft, die Muskeln zu stärken.
The repetition of this exercise helps strengthen the muscles.

The noun 'Wiederholung' (repetition/review) comes from the verb 'wiederholen' (to repeat). This is made up of 'wieder' (again) and 'holen' (to fetch) and describes the idea of doing or experiencing something again.
Die Wiederholung der Grammatikregeln ist sehr wichtig.
The review of the grammar rules is very important.
You can recognize the exact meaning from the context. In connection with learning, it refers to study material (m03); with media, to broadcasts (m02); and with actions in general, to doing something again (m01).
Zur Wiederholung schauen wir uns die letzte Lektion an.
For review, we'll look at the last lesson.
In the general sense, the word is often used to describe negative things one wants to avoid. Typical phrases are 'die Wiederholung eines Fehlers' (the repetition of a mistake) or 'eine ständige Wiederholung derselben Argumente' (a constant repetition of the same arguments).
Wir müssen eine Wiederholung dieses Problems unbedingt vermeiden.
We absolutely have to avoid a repetition of this problem.
When it comes to media, the preposition 'in' or the verb 'laufen' (to air/run) is often used. A program is then 'in der Wiederholung' (in reruns) or 'läuft als Wiederholung' (airs as a rerun).
Der Film lief gestern Abend nur als Wiederholung.
The film only aired as a rerun last night.
When studying, 'Wiederholung' (review) is often used with the preposition 'zur' to express purpose. You do something 'zur Wiederholung' (for review).
Zur Wiederholung lesen wir den Text noch einmal laut.
For review, we'll read the text aloud once more.
practice / exercise
'die Übung' and 'die Wiederholung' can both help with learning. 'die Übung' means that you actively train a skill, often with exercises. 'die Wiederholung' means that you do something again or go over material you have already learned. A repetition or review can be part of an exercise, but it is not automatically a new task. Learners may confuse the words because you practice by repeating things. As a practical rule: for specific tasks or training, 'Übung' fits; for going over familiar material again, 'Wiederholung' fits.

Vor dem Test plant Finn eine kurze Wiederholung der wichtigsten Regeln.
Before the test, Finn plans a short review of the most important rules.
Vor der Prüfung macht Max jeden Abend eine Übung zur Grammatik.
Before the exam, Max does a grammar exercise every evening.