To be or not to be: that is the question:

is possibly the most famous quotation from the theatre.  It is from Shakespeare’s Hamlet.

File:Garrick as Hamlet.jpg

David Garrick as Hamlet
Photo credit Wikimedia Commons

What a performance!
This sounds like praise for a stage show, but is usually meant to imply that someone has been making a mountain out of a molehill.

Make a production of something has a similar meaning.  There is a lot of work involved in producing a play.

Making a drama out of a crisis is another saying meaning making a lot of fuss about something which has happened.

Props is short for properties, which are looked after by the property-master.

The stage-manager organises the furniture, scenery and lighting to keep the play running how it should back-stage.  These words have migrated to everyday life, where an organising person may have stage-managed a meeting and committee members may have done a lot of work behind the scenes.

To steal the limelight is not a recommended ploy for an extra in a play.  Limelight was an old way of illuminating the stars of the show.  Now they are under the spotlight in order to receive the most attention.

To steal someone’s thunder is another phrase which has its origin in theatre.  A device was invented to represent thunder in a play.  An explanation of the derivation of the phrase appears in the Inky Fool’s blog.

Actors and actresses are traditionally very superstitious.  Instead of wishing each other luck before a performance, they are likely to say: “Break a leg!”

Tread the boards refers to the floorboards on the stage.

Comic relief has become synonymous with fundraising like Children in Need.  Its origin is in play writing, where after a particularly sinister scene there is something much lighter.  Inthe Scottish play the porter (gatekeeper) provides this.

The show’s not over until the fat lady sings.
Operatic singers tend to be rather large!

To have something off pat
means to have learned it by heart.  A salesman may have his patter.

The Bible gives another example of counterintuition.  Actors and those who speak publicly prepare beforehand.  In Mark 13:9-11 Jesus tells his disciples to expect persecution, but “do not worry beforehand about what to say.  Just say whatever is given to you at the time, for it is not you speaking, but the Holy Spirit.” (NIV)