An operation that reverses a previous action.
"Clicking the undo button reversed the accidental deletion of the file."
In plain English: An undo is an action that reverses something you just did, like taking back a text message before it gets sent.
"The undo button is always in my undo list, ready to fix any mistakes I make online."
To reverse the effects of an action.
"You can undo the changes you made to the document by pressing Control and Z at the same time."
In plain English: To undo something means to reverse an action and return things to how they were before you did it.
"I tried to undo my mistake by calling him back immediately."
Usage: Use undo as a verb to describe reversing a specific digital or physical action, such as canceling a text message or taking back a mistake. This term is commonly paired with computer commands but applies generally whenever you need to negate something that has already been done.
Misspelling of undue.
"The editor marked the document as containing a misspelling of undue, noting that undo was used incorrectly in that context."
The word "undo" comes from Middle English and Old English, where it originally meant "to reverse an action." It is formed by combining the prefix un- with the verb do.