What does the "erythematosus" in sle mean?

Redness: Erythematosus simply means redness. This is from the inflammation which is part of lupus an can show up as a rash on the skin especially in certain parts of the body like the face in a butterfly like pattern.

Redness: Redness of the skin, usually in the form of a facial rash.

Red wolf: Lupus means wolf. Erythema refers to redness, meaning the redness of the skin rash. W.P. Kinsella, a canadian author, wrote a fiction book, "red wolf, red wolf.".