Entomology definition of Thorax: the second or intermediate region of the insect
body, bearing the true legs and wings: made up of three rings,
named in order, pro-, meso-, and meta-thorax: when the pro-thorax
is free as in Coleoptera, Orthoptera, and Hemiptera, the term
thorax is commonly used in descriptive work for that segment
only: in Odonata, where the prothorax is small and not fused with
the larger and united meso- and meta-thorax, the term thorax is
commonly used for these latter two united, excluding the
prothorax.