Turnout

An external rotation of the leg that comes from the hips, causing the knee and foot to turn outward, away from the center of the body. This rotation allows for greater extension of the leg, especially when raising it to the side and rear. Turnout is essential to classical ballet technique and is the basis on which all ballet movement follows.

 

In the image, the teacher is demonstrating the action of rotating the legs from the hips, from feet in parallel to a turned-out first position. Make sure your core is tight and you're not sticking out your butt!