What is "principal boy"

In pantomime, a principal boy role is the young male protagonist of the play, traditionally played by a young actress in boy's clothes.

The tradition grew out of laws restricting the use of child actors in London theatre, and the responsibility carried by such lead roles. A Breeches role was also a rare opportunity for an early 20th century actress to wear a costume revealing the legs covered only in tights, potentially increasing the size of the audience. The practice of having a female play the principal boy has become less common, as further outlets are sought for the talents of young male popular stars and actors.

Although not written as a pantomime, Peter Pan, or The Boy Who Wouldn't Grow Up is often produced as one with the tradition of a female principal boy continuing.