Definition of "firefly"

firefly

noun
plural fireflies
1. Any beetle of the family Lampyridae, which exhibit bioluminescence during twilight.
  Quotations
  Fireflies are the best-known insects that produce light. […] Many fireflies use their light to communicate, particularly at mating time when males and females have to get together.
  2000, Exploring Life Science, 2: Bats—Cave Life, Marshall Cavendish, page 96
  The luciferins are different in different species and today both the luciferin and luciferase in the firefly are available in the crystalline form.
  2004, B. V. David, T. N. Ananthakrishnan, “Chapter 20: Bioluminescence”, in General and Applied Entomology, 2nd edition, Tata McGraw-Hill, page 130
  Various other luciferase genes, especially the firefly luciferase gene, are also used for the study of gene regulation. […] The classic use of bioluminescence, however, is the use of a luciferin-luciferase mixture from fireflies as an assay for ATP.
  2007, Lars Olof Björn, Helen Ghiradella, “23: Bioluminescence”, in Lars Olof Björn, editor, Photobiology: The Science of Life and Light, 2nd edition, Springer, page 607