What is the symbol called to correct copy repeated in a sentence?

The symbol used to correct copy repeated in a sentence is called a stet.

It looks like this: stet (Latin for "let it stand").

It is used in proofreading to indicate that a change made by an editor or proofreader should be ignored and the original text should be left as is.

For example, if a proofreader mistakenly deletes a word, they might write "stet" next to the deleted word to signal that it should be restored.