Theatre Glossary: A

Amateur Actors, Ad-Libbing and Antagonists - What could possibly be happening?

Welcome, to the very first instalment of our Theatre Glossary series - where we lovingly decode all the weird and wonderful terms that theatre folk throw around like confetti at a finale. 

Whether you’re new to the world of theatre, want to impress your local am-dram society, or just need to finally understand what your stagey mate means by "She had an ad-lib in Act One when she came on stage right through the pros," this series has your back. 

So, silence your phone, no photos, and let’s begin with the letter A! 

ACT 

Nope, not the verb (though we love a bit of drama). In theatre, an act is a major section of a play or musical. It’s kind of like how football has halves, but with fewer red cards and more jazz hands. 

Most modern shows are split into two acts, separated by the interval (aka your chance to race to the bar). Some plays have three acts, and the really old-school epics might go all the way to four or five, but pack snacks if you're seeing one of those. 

Acts are broken down further into scenes, and usually end with something dramatic enough to make you need that gin and tonic at the interval. 

ACTOR / ACTRESS 

The lovely humans who say the lines, wear the costumes, and occasionally trip over the set. 

“Actor” is now often used as a gender-neutral term for performers of any identity - but you’ll still hear both versions. Either way, these are the folks doing the acting. Unless they’re corpsing (see Theatre Glossary: C). 

AD-LIB 

Short for “ad libitum,” Latin for at one’s pleasure, this is theatre code for “they made it up on the spot.” 

Usually happens when someone forgets their line, misses an entrance, or a prop decides to fall apart mid-scene. 

Done well, it can save a show. Done badly... well, at least it’s memorable. 

AD 

Not a plug for shampoo. This in fact stands for Assistant Director - the person who supports the main director by helping with rehearsals, giving notes, or stepping in when the director is stuck in traffic / crying over a tech run / busy explaining to the lead actor that yes, you do have to sing it that high. 

AISLE 

Simple one! The gap between seats in the theatre where the usher glares at you for arriving late. Also, where the more dramatic entrances/exits happen in immersive shows. 

ALTERNATE 

This performer steps into a major role regularly - not just if the lead is off sick with laryngitis. 

Think of it like a scheduled understudy. In big shows (looking at you, Wicked), the alternate might do every Thursday matinee so the main star can rest her vocal cords / go cry in a Pret a Manger. Note: This is usually a professional role, they are very rare in amateur theatre. 

AMATEUR 

As in Amateur Theatre - the backbone of the performing arts! 

Don’t be fooled by the name. Amateurs might not be paid, but they often work just as hard (if not harder) than the pros. Expect glitter, passion, and someone who once taught GCSE chemistry absolutely smashing it as Javert. 

AMPHITHEATRE 

Going way back with this one. 

An amphitheatre is a round or oval open-air venue used in ancient Greece and Rome for performances, battles, and the odd lion-feeding (thankfully, we've dropped that last one). Modern amphitheatres still exist and make for gorgeous summer Shakespeare settings, weather permitting, of course. 

ANTAGONIST 

The baddie! Or at least, the one making life hard for the protagonist (See Theatre Glossary: P). 

Think Scar in The Lion King, Javert in Les Mis, or the front-row audience member who checks their phone mid-song whilst eating crunchy snacks... 

APRON 

No, not the kitchen kind. In theatre, the apron is the part of the stage that juts out in front of the proscenium arch (See Theatre Glossary: P, again). 

It’s where monologues happen, ghosts appear, and actors sometimes fall off. 

ARE YOU DECENT?

A classic backstage cry, often shouted by someone about to enter a shared dressing room or quick-change area.

Rough translation: “Please don’t be naked, I’m coming in.” It’s theatrical etiquette, darling, and just good manners - especially during a frantic change between Scene 4 and Scene 5 when someone’s halfway into a corset and cursing Velcro.

ARRANGEMENT

In musical theatre, this refers to the musical structure of a song - how it’s arranged for instruments or voices. A new vocal arrangement might add lush harmonies or shift a solo to a duet; an orchestral arrangement might transform a simple tune into a sweeping ballad with strings and brass. It's like the musical version of costume design: same material, different sparkle.

ASIDE 

A sneaky little line said directly to the audience, often unheard by the other characters. Perfect for spilling tea, revealing secret thoughts, or delivering sass. Think Fleabag, but on stage and with less guinea pig-themed cafés, or for you more distinguished older folk out there, think Up Pompeii with some witty Frankie Howard looks to the camera. 

ASM (Assistant Stage Manager) 

The backstage hero. They make sure props are in place, scenery moves when it should, and actors aren’t found napping in the wings. If the show runs smoothly, thank an ASM. If it doesn’t… also thank the ASM, they’ve had a day. 

ATMOSPHERE

This isn’t just the vibe, theatre runs on atmosphere. This is the mood created onstage through lighting, sound, music, staging, and performance. Whether it’s spooky fog and creaking floorboards or a warm glow and gentle strings, atmosphere makes a scene feel right.

AUDIENCE 

That’s you! Or us. Or your nan who came because she thought Sweeney Todd was a nice musical about a baker. 

An audience’s energy is vital. Laugh, clap, gasp, but for the love of all things theatrical, do not unwrap sweets during a soliloquy (See Theatre Glossary S... wow there are lots of words aren’t there?). 

AUDITION 

The thrilling, nerve-wracking ritual of proving you’re the perfect Elphaba, even if you’ve only had two hours’ sleep and your backing track is skipping. 

Actors will do many of these. Some go well. Some… become dinner party stories. 

AUDITORIUM 

The main part of the theatre where the audience sits. 

Not to be confused with the bar, the dressing room, or the loo. Though let’s be real, we’ve all had moments of panic in the wrong one. 

AVANT-GARDE 

French for “ahead of the guard,” this term describes experimental, boundary-pushing theatre. 

Think performance art with projections, no dialogue, and probably someone wearing papier-mâché. It’s bold, it’s brave, and sometimes… it’s very confusing. But that’s the point. 

And there you have it: the first alphabetical adventure through the theatre world! From actors to amphitheatres, ASMs to asides, the letter A has set the stage beautifully. 

Check out Theatre Glossary: B, where we’ll explore backdrops, blocking, and the bane of every director’s existence - bad accents (we joke). 

Until then, break a leg (but not literally), and remember: if you don’t know the word for something in the theatre, just fake it with enough confidence and jazz hands.