pleura, from Greek side, rib) is a lateral sclerite of thoracic segment of an insect between the tergum and the sternum.
[1] While the tergum is positioned on the top (dorsal), and the sternum on the bottom (ventral), the pleuron is positioned to the side (lateral).
The terms pro-, meso- and metapleuron are used respectively for the pleura of the first, second and third thoracic segments.
A pleuron usually consists of a epimeron and an episternum.
[2] An epimeron is the posterior (back) sclerite of the pleuron, and an episternum is the anterior (front) sclerite.