In this scene from Swan Lake, the corps de ballet is forming a "V" at the front of the stage. They are directing attention to the principal dancer in the spotlight. The dancers behind her are also corps de ballet and form a backdrop.
In ballet, the corps de ballet (from French, body of the ballet) is the group of dancers who are not soloists. They are a permanent part of the ballet company and often work as a backdrop for the principal dancers. A corps de ballet works as one, with synchronized movements and corresponding positioning on the stage. Specific roles are sometimes made for the corps de ballet, such as the Snow Corps de Ballet and the Flower corps in Nutcracker.