Stet is a Latin word used by proofreaders

Proofreading

Proofreading is the reading of a galley proof or computer monitor to detect and correct production-errors of text or art. Proofreaders are expected to be consistently accurate by default because they occupy the last stage of typographic production before publication.-Traditional method:A proof is...

 and editors

Copy editing

Copy editing is the work that an editor does to improve the formatting, style, and accuracy of text. Unlike general editing, copy editing might not involve changing the substance of the text. Copy refers to written or typewritten text for typesetting, printing, or publication...

 to instruct the typesetter

Typesetting

Typesetting is the composition of text by means of types.Typesetting requires the prior process of designing a font and storing it in some manner...

 or writer to disregard a change the editor or proofreader had previously marked.

This convention is usually marked by writing and circling the word stet above or beside the unwanted edit and underscoring the selection with dashes or dots. Alternatively, a circled tick (check mark) may be used in the margin.

In connection with this usage, stet is also sometimes used as a verb, e.g., "Stet that colon."