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.
The leading dancer in a Corps de ballet is a Coryphée. Specific roles are sometimes made for the corps de ballet, such as the Snow Corps de Ballet and the Flower Corps in The Nutcracker.