The word "scapula" refers to the flat bone located on your upper back, also known as the shoulder blade. It connects the upper arm bone (humerus) to the collarbone (clavicle) and helps with shoulder movement. Full definition
For instance, if you have an internal rotation of the arm, which is very typical to many people with kyphotic posture, this position of the arm can create a protraction of scapula and this might affect or even harm your shoulders while you do various asanas. (yogauonline.com)
• Don't put too much of the tension on your biceps and focus on scapula retraction instead. (fitnessandpower.com)
The ones that are needed are the depressed and retracted scapula. (ashotofadrenaline.net)