Blush describes the responsive reddening of the skin caused by blood vessels dilating. This can happen on many parts of the body, but is typically connected with the face as this is where it is often most obviously seen - this tag is used to cover all blushing, but when used alone refers to facial blushing.
While blush shouldn't realistically be visible through fur, feather, or scales, it's frequently used and accepted by suspension of disbelief for added expressiveness.
Related tags
Body location
Face and Head Blush
Symbolic
Intensity
Other
See also