Halteres n. pl. : Balancers; the rudimentary hind wings of Diptera.

Example:


Taxonomy
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Defination from the web:
halteres visible below the wings as appendages, about as long as the animal's antennae, with knobs on the end. Halteres (pronounced /hælˈtɪəriːz/; singular halter or haltere) are small knobbed structures found as a pair in some two-winged insects. ...