(1) To make a repair while running. It often refers to modern disk drives, which mark sectors in poor condition as bad and remap the data to spare sectors. In this case, the procedure is hidden from not only the user, but the operating system as well. See
hot swap.
(2) Microsoft's term for a bug fix, which is accomplished by replacing one or more existing files (typically DLLs) in the operating system or application with revised versions. See
QFE.