The term morbilliform refers to a rash

Rash

A rash is a change of the skin which affects its color, appearance or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracked or blistered, swell and may be painful. The causes, and...

 that looks like measles

Measles

Measles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...

. The rash consists of macular lesion

Lesion

A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...

s that are red and usually 2-10 mm in diameter but may be confluent in places.

Patients with measles will have the rash but there are other syndromes and infections that will display the same symptom such as patients with Kawasaki disease

Kawasaki disease

Kawasaki disease , also known as Kawasaki syndrome, lymph node syndrome and mucocutaneous lymph node syndrome, is an autoimmune disease in which the medium-sized blood vessels throughout the body become inflamed. It is largely seen in children under five years of age...

, meningococcal petechiae-Waterhouse-Friderichsen syndrome

Waterhouse-Friderichsen syndrome

Waterhouse-Friderichsen syndrome or hemorrhagic adrenalitis or Fulminant meningococcemia, is a disease of the adrenal glands most commonly caused by the bacterium Neisseria meningitidis. The infection leads to massive hemorrhage into one or both adrenal glands...

, Rubella

Rubella

Rubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...

, Echovirus 9

Echovirus

An ECHO virus, is a type of RNA virus that belongs to the genus Enterovirus of the Picornaviridae family...

, drug hypersensitivity reactions (in particular with certain classes of antiretroviral drug

Antiretroviral drug

Antiretroviral drugs are medications for the treatment of infection by retroviruses, primarily HIV. When several such drugs, typically three or four, are taken in combination, the approach is known as Highly Active Antiretroviral Therapy, or HAART...

s, such as Abacavir

Abacavir

Abacavir is a nucleoside analog reverse transcriptase inhibitor used to treat HIV and AIDS. It is available under the trade name Ziagen and in the combination formulations Trizivir and Kivexa/Epzicom...

 and Nevirapine), or other conditions may also have a morbilliform rash.