1. A genus of ringworm fungi of the family Moniliaceae that have hyaline single-celled spores and are parasitic in the skin and hair follicles of humans and lower mammals.
2. A genus of parasitic fungi that lives in or on the skin or its appendages (hair and nails) and is the cause of various dermatomycoses and ringworm infections.

Species that produce spores arranged in rows on the outside of the hair are designated ectothrix; if the spores are within the hair, they are termed endothrix.