The Introduction because when you read a book the beginning is called a introduction.
That would be "Opening Night." Keep in mind that there are usually two openings for major shows: opening night of previews, which run for about two weeks in order to give the management time to work out the final kinks, and then the opening night of the actual run of the show.
Strictly speaking, the opening night is the first performance of a production, including a new production of a play which has been produced before. The first performance of the play is called the premiere.
Be careful here. You are thinking of a prologue, probably, but in Shakespeare's play Richard III, Richard starts the play with a speech by an actor to the audience, but it is nevertheless not a prologue. In order to be a prologue, the speech must be delivered by someone who is not a character in the play, who will not interact with the other actors. It does not have to be by someone called Chorus (although that name is used in Romeo and Juliet and Henry V); the prologue to Pericles is delivered by Gower and that to Henry IV Part II is delivered by Rumour.
The first part of a play could be called a few different things:
The prologue
Act one
The opening
The opening speech, as the phrase implies, is the first speech that any character delivers in the course of the play.
Prologue
Prologue
Introduction
the opening
Prologue
Epilogue
In The Tragedy of Julius Caesar, a play by Shakespeare, this is (mostly) the beginning of an often quoted speech by Mark Antony. The speech begins:"Friends, Romans, countrymen, lend me your ears;I come to bury Caesar, not to praise him."
Social Speech
This kind of speech is called a filibuster.
The - article first - adjective play - noun
A speech at the beginning of a play is called a prologue.
This is called a prologue.
Prologue
Prologue
It is a prologue.
Epilogue
The speech at the end of a play is called an "epilogue." It is a final address to the audience by one of the characters or sometimes by the playwright, offering closing remarks or reflections on the events of the play.
Epilogue
It's called a "phrasal adjective" as it modifies the meaning of the sentence.
The Introduction because when you read a book the beginning is called a introduction.
Abraham Lincoln gave the, "Four score and seven years ago," speech.
You are referring to William Shakespeare, but it's not a play-- it's a speech from "Hamlet"-- a special kind of speech called a soliloquy (when a character steps out in front of the stage and gives a speech all by himself or herself, usually about some issue that is very important in the play).