1. Insects that live only for a day in their winged form.
2. Somethings that are transitory and without lasting significance; lasting a day.
3. Collectible items that were originally designed to be short-lived: "She's a collector of ticket stubs, movie passes, bus transfers, and other ephemera."
4. A family in the insect order Ephemeroptera, the mayflies.

The type genus, Ephemera, and others are associated with asthma because of the sensitization from inhalation of cast skins and bits of dried materials from the large swarms of these abundant insects.