It originates from old superstitions that to wish an actor good luck would tempt fate and encourage the Gods to cause bad luck as opposed to good. So this in turn has led to people to use negative expressions to wish their luck instead of positive messages. For example in France they say Merde! Which in English means Crap! The German expression is Hals und Beinbruch which literally means "neck and leg fracture" and leads people to believe that the English expression came from the German. It also may have stemmed from wishing someone a 'big break' as in good luck leading to success, this show could be their 'lucky break'! so to speak, but overtime it led to misinterpretation and the term 'break a leg!'. Another theory is that the successful French actress Sarah Bernhardt had only one leg and so to be as good as her would be very lucky.
The term “break a leg” may be traced in origin to Elizabethan language. To break a leg in Shakespeare’s time literally meant to bow, while bending the knee. Since only a successful actor would break a leg on stage and receive applause, this phrase would have, in effect, been a wish of good luck and good performance to the actor.
It kinda means good luck!
It means do good
Yes it means good luck.
Break a leg means good luck in theatre
Cute answers people, but wrong!!! They say break a leg, meaning good luck or do well due to the design of the old curtains. Curtains in the theater used to have wooden rods "legs" at the bottom. And if encore bows were needed, sometimes the repetitive rising and lowering of the curtain would cause them to break. Hence break a leg means do so well that you get the encores and literally break a leg!