die Korrektur
correction
The process of checking and improving errors in a text, calculation, or piece of work.
Die Korrektur der Klausuren nimmt viel Zeit in Anspruch.
Correcting the exams takes a lot of time.

correction
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correction
The process of checking and improving errors in a text, calculation, or piece of work.
Die Korrektur der Klausuren nimmt viel Zeit in Anspruch.
Correcting the exams takes a lot of time.

'Die Korrektur' (the correction) is the noun that belongs to the verb 'korrigieren' (to correct). When someone corrects a text, the result is the correction of the text.
Der Lehrer korrigiert die Aufsätze. Die Korrektur wird eine Woche dauern.
The teacher is correcting the essays. The correction will take a week.
Common verbs used with 'Korrektur' (correction) are 'Korrektur lesen' (to proofread a text for errors) and 'Korrekturen vornehmen' (to make corrections).
Könntest du meine E-Mail bitte Korrektur lesen, bevor ich sie abschicke?
Could you please proofread my email before I send it?
'Die Korrektur' (the correction) in the singular often describes the entire process of improving something. 'Die Korrekturen' (the corrections) in the plural, on the other hand, usually refers to the individual changes that were made.
Die Korrektur meiner Bachelorarbeit hat vier Wochen gedauert.
The correction of my bachelor's thesis took four weeks.
In financial jargon, 'Korrektur' (correction) has a special meaning: a significant, but usually temporary, decline in stock prices after a period of growth. This meaning is limited to specialized texts.
Analysten halten eine baldige Korrektur an der Börse für wahrscheinlich.
Analysts consider a correction on the stock exchange likely soon.
change
'Änderung' and 'Korrektur' can both refer to a part of a text, calculation, or piece of work that you change. The difference is the reason: a 'Korrektur' eliminates an error. An 'Änderung' does not have to happen because of an error; it can also be a new idea, a new plan, or a different wish. Learners may confuse the words because every 'Korrektur' is a kind of 'Änderung'. But not every 'Änderung' is a 'Korrektur'.

Nach der Korrektur waren keine Rechtschreibfehler mehr im Brief.
After the correction, there were no spelling mistakes left in the letter.
Vor dem Termin war noch eine Änderung im Plan nötig.
Before the appointment, one more change to the plan was necessary.