the gods at the Comedy Theatre, London, 1949
source: Historic England – The Theatres Trust

Via Middle French galerie, the noun gallery, attested in the late 15^th century, is from the medieval Latin of Italy galeria, an alteration of medieval Latin galilaea, designating a porch at the entrance of a monastery’s church—hence English galilee, denoting a porch or chapel at the entrance of a church.

This was a figurative use of classical Latin Galilaea, denoting Galilee, the northern region of ancient Palestine where Jesus is said to have lived and travelled. In the scriptures, Galilee was considered to be the land of the Gentiles (in the gospel of Matthew, 4:15, there is “Galilee of the Gentiles”) as opposed to Judaea, the land of the chosen people. Similarly, the porch of the church was the place where the people to convert were gathering, as opposed to the church itself.

Since the 17^th century, the highest seats in a theatre and the persons who occupy them have been called the gallery.

As this was where the cheapest seats and the least refined members of the audience were found, to play to, or for, the gallery, or the galleries, came to mean to act in an exaggerated way in order to appeal to popular taste.

In the epilogue to his lost play The Scholars (printed with his poems in 1649), the English poet and army officer Richard Lovelace (1618-57) noted the division made by money inside theatres:

The stubborne author of the trifle, Crime,
That just now cheated you of 2 hours’ time,
Presumptuous, it lik’t him, began to grow
Carelesse, whether it pleased you or no.

But we who ground th’ excellence of a Play
On what the women at the dores wil say,
Who judge it by the Benches, and afford
To take your money ere his Oath or word
His Schollars school’d, sayd if he had been wise
He should have wove in one, two Comedies;
The first for th’ Gallery, in which the Throne
To their amazement should descend alone,
The rosin-lightning flash, and Monster spire
Squibs, and words hotter then his fire.

Th’ other for the Gentlemen oth’ Pit,
Like to themselves, all Spirit, Fancy, Wit,
In which plots should be subtile as a Flame,
Disguises would make Proteus stil the same:
Humours so rarely humour’d, and exprest,
That ev’n they should thinke ’em so, not drest;
Vices acted and applauded too, Times
Tickled, and th’ Actors acted, not their Crimes,
So he might equally applause have gain’d
Of th’ hardned, sooty, and the snowy hand.

The earliest instance of the phrase that I have found is from The Liverpool Mail (Lancashire) of 16^th December 1837:

Mr. Balls, whose name we have here incidentally introduced, is one of the best “stars” brought down this season. His acting is gentlemanly, lively, and varied. He never over-acts,—it seems as if natural impulse, checked by good taste, carried him through each character exactly as the part demanded. His figure, face, and voice are all in his favour,—he has great versatility, also, and he does not condescend to the vulgar claptrap of “playing to the gallery” for senseless and vociferous applause.

The Era (London) of 24^th April 1859 gave an account of the Fourteenth Annual Festival of the Royal General Theatrical Fund, celebrated the previous Monday; the actor and playwright Charles James Mathews (1803-78), chairman, declared in the closing speech:

Gentlemen,—I have only one more toast to propose to you, a last toast though not least, in our “dear love”—a remark which I do not wish to palm off upon you as my own. I do not profess to be original after eleven at night. My hours of performing are generally from seven to eleven, about which time I generally find I have had enough of it. (Laughter.) It is the health of the fair ladies who have done us the honour of assisting and gracing this hall this evening. (Cheers.) I am not generally in the habit of playing to the galleries, but if they always contain the same occupants that I see before me to-day, and which I cannot see behind me, I should certainly change my style of acting and play entirely to them. Gentlemen, I propose to you “The health of the Ladies.”
The toast was drunk upstanding, with three times three cheers.

Because they occupy the highest seats, these members of the audience have also, since the 18^th century, been called the gods, a name later applied to the gallery itself. Similarly, in French, the theatre gallery is called le paradis; another name is le poulailler, the henhouse.

Set among the Parisian theatre scene of the 1820s and 1830s, Les Enfants du Paradis (The Children of the Gods) is a 1945 French film directed by Marcel Carné, written by Jacques Prévert, starring Arletty, Jean-Louis Barrault and Pierre Brasseur.

Other words or phrases of theatrical origin:
to be decent (sufficiently clothed to see visitors)
malapropism
claptrap
cloak-and-dagger
Mrs Grundy
Paul Pry
Mummerset
simon-pure
fedora
Box and Cox
Hamlet without the Prince
slapstick
old chestnut
to steal someone’s thunder
bums on seats