What is "vesper bat"

n. A member of a family of bat, the Vespertilionidae.

Vesper bats (family Vespertilionidae), also known as evening bats or common bats, are the largest and best-known family of bats. They belong to the suborder Microchiroptera ( microbats). Over 300 species are distributed all over the world, on every continent except Antarctica. It owes its name to the Latin word ("bat"), from , meaning "evening".