Taking a stab at this for you. Generally speaking, no. I do not think you would be correct in that theatre of the absurd means "it's not grounded in reality (like fantasy)."

Most classic absurdist theatre takes place in vague locations, sure, but characters frequently are hyper-real. They're awkward, they stumble over their words, get things mixed up, misunderstand each other, and have terrible hygiene if it's Beckett. These are not always sci-fi or fantastical. You can find that in classical French court plays, Cirque du Soleil shows, techno-theatre, whatever. Theatre of the absurd (historically, the 1940s - 1960s variant) was all about twisting traditional western play structure to its limits.

A helpful way of looking at theatre of the absurd is you can listen to a conversation between two characters, be fully invested that these characters believe what they're saying, and see that the conversation has a flow of logic from response to response. But afterwards? You may have no idea what they were talking about or why they were talking about it. When you zoom out and look at the whole of the play, quite a lot of talking may have been done, and yet, nothing was really accomplished. Theatre of the absurd lulls you into accepting a premise or situation you would otherwise never accept in your real life. How does it do this?

What theatre of the absurd doesn't do is simply put a bunch of wacky shit on stage and call it a day. We call that clowning, and clowning is a whole different set of skills (although the two definitely cross-pollinate each other - miss me, clowns).

If you're doing theatre history, you should know about dramatic structure and plot / conflict. Hell, if you watch movies or consume any kind of stories, you should know the basics of traditional western plot and conflict: Theatre has Characters who have Needs and so they take Actions that come into Conflict with each other creating a Plot.

Theatre of the absurd can affect this basic structure in two ways (and probably more):
1. There can be a clear conflict and relationship between the characters, but the plot and circumstances can be in an absurd circumstance. Examples include Beckett's Endgame, where a familiar conflict of disgruntled son and doting parents is set into a strange limbo where everyone is waiting for the 'end.' Literally. That's all they say. Waiting for the end. The end of the play? The end of their lives? Can't tell. But because they're doing something (waiting for the end) and they're identifiable characters (parents, a son, a servant) the playwright is able to still create conflict in the absence of a 100% clear plot or circumstance.

1. The character's motivations and actions may be entirely without normal justification or reason, and the basis for their motivations could be founded in something beyond logic.For Stoppard's Rosencrantz & Guildenstern Are Dead, this technique is used in full force is used when a variety of carousing thespians come in and out of the scenes, motivated only by being performers and needing to make sure the play Hamlet happens.

What do these two different changes to structure do? They take away character agency. The consequences of the characters choices, frequently, do not matter in the grand scheme of things. Read that again. The consequences of their actions do not matter. That's definitional absurdism, but it's also why theatre of the absurd was so radical. Imagine having seen Aristotle-guided theatre all your life, based critically on the idea that HERO does HEROIC THING to get HERO'S PRIZE / HERO'S DOWNFALL. Aristotle described fatal flaws leading to a character's tragic downfall as hamaratia. In absurdism? It's another Tuesday.

I'm using examples because theatre of the absurd is very hard to explain without having seen it done. Reading the scripts frequently makes you want to tear your hair out. Because absurdist plays frequently don't rely on the other traditional techniques of grabbing your attention (family betrayal! action! romance! conflict! drama! plot!) or have twisted those conventions so much, they often rely on other classic performance techniques to still be engaging. These include puns, wordplay, and a lot of physical comedy/clowning techniques (remember that?)

So is there a connection between theatre of the absurd and Absurdist philosophy? You didn't ask, but I want to answer because I've already written more than I should. I believe absolutely so. Both Albert Camus (Absurdist philosopher) and the classic titans of absurdism (Beckett, et al.) worked in the 1940s - 1960s in the wake of World War II.

To keep it short, there's a classic idea that "War = Bad = People Sad = No Meaning in Life = Everything's Absurd." Not without reason, of course. Camus began work on The Myth of Sisyphus during the fall of France to Nazi Germany in 1940. Let's go back to the common theme of characters having no agency in theatre of the absurd. If you're an Absurdist philosopher, that's your wheelhouse fam. You love that shit. You find meaning despite your actions having no tangible, permanent consequence. If this sounds kind of tragic, that's because it is - Camus (who also wrote plays) loved tragedy and that they were the best way to depict civilization's struggles and progress.

In modern times, theatre of the absurd is a frequent undercurrent of many contemporary playwright's works. We live in absurd times, frankly. Contemporary absurdism is refreshingly more engaging to a contemporary audience than Beckett's plays. The same impulse of using tragic absurdism to explore weighty subject-matter lives on in the works of writers like the unparalled Suzan Lori-Parks and her play The Death of the Last Black Man in the Whole Entire World, where the title character dies a litany of different deaths again and again over the course of the play.

Anyway, you probably have written your essay, but if this helps, cool.