What is Theatre?

In my opinion theatre is any performance with an audience. This doesn't have to be in a conventional theatre space and instead it can be anywhere that there are spectators.
It can be a piece of performance ranging from naturalistic to experimental, physical to purely voice, maybe even only the use of sound or in fact all of it combined together.

I do however feel the performance must have a purpose, be it to entertain or inform. Ideally it must make people think as it is a great means of expressing hard hitting/taboo subjects to a large audiences and as an actor, it is our duty to do this. However on the occasion it can be nice to watch a piece of light hearted entertainment as it can be a source of escape for audience members, although this can be achieved through work that is informative. 
On the whole I think theatre is way for audiences to escape regular life and immerse themselves reality before them. It is a greats way to expand people's thinking, not only being a pleasant sight but also helping both the actors and audience to become more opened minded to different topics. 

In some so-called traditional methods of acting I do feel that some of theatre's purpose is lost. With actors wanting to get their performances right they remove their abilities to respond truthfully and instinctively, therefore removing the audience will to suspend their beliefs and a topic which maybe crucial to progress. 
An audience member, to me, must be willing to suspend their belief in order to connect with the performance and for this to occur the actors must be able to create an environment which allows them to do so. I've seen performances with thousands of pounds of set and I've seen others with no set at, of which both let me fully engage with the piece. This suggests to me that a performance is not about the best most accurate set, lighting or music, or in fact having any of these things at all, instead theatre focuses on the actors and what they can do to make an audience invest in the performance.

To me theatre is what actors can do to an audience to make them feel.

The Spurt of Blood: Antonin Artaud - TRANSLATED BY RUBY COHN

CHARACTERS
A YOUNG MAN
A WET-NURSE
A YOUNG GIRL
A PRIEST
A KNIGHT
A COBBLER
A BEADLE
A PEDDLER
A BAWD
A HUGE VOICE
A JUDGE


YOUNG MAN: I love you and everything is beautiful.
YOUNG GIRL: [With quavering voice] You love me and everything is beautiful.
YOUNG MAN: [In a lower tone] I love you and everything is beautiful.
YOUNG GIRL: [In an even lower tone] You love me and everything is beautiful.
YOUNG MAN: [Leaving her abruptly] I love you. [Silence] Face me.
YOUNG GIRL: [As before standing opposite him] There.
YOUNG MAN: [In an exalted high-pitched voicej I love you. I am great, I am lucid, I am full, I am dense.
YOUNG GIRL: [In the same high-pitched voice] We love each other.
YOUNG MAN: We are intense. Ah, how beautifully the world is built.

[Silence. There is a noise as if an immense wheel were turning and moving the air. A hurricane separates them. At the same time, two Stars are seen colliding and from them fall a series of legs of living flesh with feet, hands, scalps, masks, colonnades, porticos, temples, alembics, falling more and more slowly, as if falling in a vacuum: then three scorpions one after another and finally a frog and a beetle which come to rest with 
desperate slowness, nauseating slowness]

YOUNG MAN: [Crying with all his strength] The sky has gone mad.
[He looks at the sky] Let's hurry away from here. 
[He pushes the Young Girl before him]

[Enter a medieval Knight in gigantic armor, followed by a Wet-Nurse holding her breasts in her hands and puffing because her breasts are swollen]

KNIGHT: Let go of your tits. Give me my papers.
WET-NURSE: [Screaming in high-pitch] Ah! Ah! Ah!
KNIGHT: Damn, what's the matter with you?
WET-NURSE: Our daughter, there, with him.
KNIGHT: Quiet, there's no girl there.
WET-NURSE: I'm telling you that they're screwing.
KNIGHT: What the Hell do I care if they're screwing?
WET-NURSE: Incest.
KNIGHT: Midwife.
WET-NURSE: [Plunging her hands deep into her pockers which are as big as her breasts] Pimp. 
[She throws his papers at him]
KNIGHT: Let me eat.

[The Wet-Nurse rushes out] [He gets up and from each paper he takes a huge hunk of Swiss cheese. Suddenly he coughs and chokes]

KNIGHT: [With full mouth] Ehp. Ehp. Show me your breasts. Show me your breasts. Where did she go?
[He runs out] [The Young Man comes back]

YOUNG MAN: I saw, I knew, I understood. Here on a public street, the priest, the cobbler, the peddler the entrance to the church, the red light of the brothel, the scales of justice. I can't stand it any longer!

[Like shadows, a Priest, a Cobbler, a Beadle, a Bawd, a Judge, a Peddler, arrive on stage]

YOUNG MAN: I've lost her: give her back to me.
ALL: [In different tones] Who, who, who, who.
YOUNG MAN: My wife.
BEADLE: [Very fat] Your wife, you're kidding!
YOUNG MAN: Kidding! Maybe she's yours!
BEADLE: [Tapping his forehead] Maybe she is.
[He runs out] [The Priest Ieaves the group and puts his arm around the neck of the Young Man]

PRIEST: [As if confessing someone.] To what part of your body do you refer most often?
YOUNG MAN: To God. 
[Confused by the reply the Priest immediately shifts to a Swiss accent]
PRIEST: [In Swiss accent] But that isn't done any more. We no longer hear through that ear. You have to ask that of volcanoes and earthquakes. We wallow in the little obscenities of man in the confession-box. That's life.
YOUNG MAN: [Much impressed] Ah that's life! Then everything is shot to hell.
PRIEST: [Still with Swiss accent] Of course.

[At this moment night suddenly falls on stage. The earth quakes. There is furious thunder and zig-zags of lightning in every direction through the zig-zags all the characters can be seen running around bumping into each other and falling then getting up and running about like crazy. Then an enormous hand seizes the Bawd by her hair, which bursts into flame and grows huge before our eyes]

HUGE VOICE: Bitch, look at your body!

[The Bawd's body is seen to be absolutely naked and hideous beneath her blouse and skirt, which become transparent as glass]

BAWD: Leave me alone, God.

[She bites God in the wrist. An immense spurt of blood lacerates the Stage, and through the biggest fiash of lightning the Priest can be seen making the sign of the cross. When the lights go on again all the characters are dead, and their corpses lie all over the ground. Only the Young Man and the Bawd remain devouring each other with their eyes. The Bawd falls into the Young Man's arms]

BAWD: [With the sigh of one having an orgasm] Tell me how it happened to you.

[The Young Man hides his head in his hands. The Wet-nurse comes back carrying the Young Girl under her arm like a bundle. The young Girl is dead. The Bawd drops her on the ground where she collapses and becomes flat as a pancake. The Wet-Nurse no longer has her breasts. Her chest is completely flat]

KNIGHT: [In a terrible voice] Where did you put them? Give me my Swiss cheese.
WET-NURSE: [Boldly and gaily] Here you are.
[She lifts up her dress. The Young Man wants to run away but he is frozen like a petrified puppet]
YOUNG MAN: [As if suspended in the air and with the voice of a ventriloquist] Don't hurt Mommy!
KNIGHT: She-devil!

[He hides his face in horror. A multitude of scorpions crawl out from beneath the Wet-Nurse's dress and swarm between her legs. Her vagina swells up splits and becomes transparent and glistening like a sun. The Young Man and Bawd run off as though lobotomized]

YOUNG GIRL: [Getting up dazed] The virgin! Ah that's what he was looking for.