What does it mean bite your thumb in romeo and Juliet?

Biting one's thumb is a gesture of contempt or defiance in Shakespeare's plays, particularly in Romeo and Juliet. In Act I, Scene I, Sampson, a servant of the Capulets, makes this gesture at Gregory, a servant of the Montagues, saying, "I will bite my thumb at them; which is a disgrace to them, if they bear it." This gesture is understood as an invitation to fight, escalating the tension and violence between the two families.