Patching is a retouching technique which involves replacing an undesirable pixel region with a patch (a drawn freehand selection area) made up of pixels sourced from another, more suitable, part of your image or another document.
Patching, like healing, blends the target pixels with the sample pixels by matching the texture, tone, and transparency of the sample pixels with the target pixels. When patching, you can also select whether to only apply the texture of the source to the target and whether there is a level of transparency applied.
The selection can act as any of the following:
As Target—pixels are modified based on the properties of the source pixels. These pixels are sourced from under the cursor anywhere outside the selected area.
As Source—pixels are used to modify the target area(s) selected.
For both, the sample can be scaled or rotated before or after it has been applied.
You can define a source in one open document and paint the sampled pixels into another open document using Set Global Source.
Once a source is defined, the Global source option becomes available from the layer selection dropdown. It will remain available until a new source is defined, even if the original global source document is closed.