Actually,
Erythema refers simply to redness of the
skin in its
medical context. One would say "Erythema was noted surrounding the
lesion."
Erythematous, the
adjective form of the same
root word, is also appropriate to describe redness, as in "The
upper extremity was erythematous distal to the
elbow."
Therefore,
Erythema Multiforme refers descriptively to the red (erythema) heterogeneous (multiforme) rash that is
characteristic of this particular
disease.