(application) Use of some kind of editor program to modify a document. Also used to refer to the modification itself, e.g. "my last edit only made things worse".
To edit something usually implies that the changes will persist for some time, usually by saving the edited document to a file, though one might open an editor, create a new document in memory, print it and exit without saving it to disk. Editing is normally done by a human but see, e.g., sed.