Most changes in the lighttable are recorded and can be reverted. This includes modifications to color labels, ratings, geo-localization, tags, metadata, orientation, copy/paste of history, or application of a style. Thanks to this recording, it is possible to undo changes or redo them to recover a previous state. Note that this undo/redo facility is unlimited in the number of steps while in the lighttable, but it is reset each time the view is switched (going to the darkroom for example).
The default keyboard shortcuts are:
Ctrl+Z : undo last modifications
Ctrl+Y : redo last undo (does nothing if undo has not been used yet)