patagium

noun, plural pa·ta·gi·a [puh–tey-jee-uh] /pəˈteɪ dʒi ə/.

1. a wing membrane, as of a bat.
2. the extensible fold of skin of certain insects or of a gliding mammal or reptile, as a flying squirrel.
3. either of two small processes on the anterior thorax, found especially among butterflies and moths.

noun plural -gia (-dʒɪə)

1. a web of skin between the neck, limbs, and tail in bats and gliding mammals that functions as a wing
2. a membranous fold of skin connecting margins of a bird’s wing to the shoulder