What makes a thing a thing? What makes it that thing in particular? Once you can answer that, you understand the essence of essentialism. Essentialism is a school of thought that cuts straight through the crap - in other words, the unessential - to find the very definition of life, the universe and everything.
It's a simple concept, but incredibly complex when you get right down to it. What is the essence of life? What makes a human a human? What makes a vase a vase and not, say, a pitcher? Essentialism attempts to define the characteristics something must have to be what it is and not something else.
For example, what makes a dog a dog? Is it the tail? Because there are many breeds with shorter or absent tails. Is it the four legs? So a canine amputee is no longer a dog? It is the ears? The wet nose? The barking? Because there are plenty of dogs without these traits, yet you would still look at them and think, "That's a dog."
Essentialism in Art
It's far from a useless exercise. Artists in particular use a form of essentialism to process information between their eyes and the canvas. Minimalist painters especially - they strip away the non-essential to show the true essence of their subjects.
Kurt Vonnegut explored this in Breakfast of Champions with the painting The Temptation of Saint Anthony by fictional painter Rabo Karabekian. He describes the painting as
"...twenty feet wide and sixteen feet high. The field was Hawaiian Avocado, a green wall paint manufactured by the O'Hare Paint and Varnish Company in Hellertown Pennsylvania. The vertical stripe was day-glo orange reflecting tape."
In the book, a small town museum paid a large amount of money to acquire the painting, and the taxpayers were angry. They didn't see it as art, thinking anyone could affix tape to a canvas and call it art. Later, defending his painting, the artist says,
"I now give you my word of honor [. . .] that the picture your city owns shows everything about life which truly matters, with nothing left out. It is a picture of the awareness of every animal. It is the immaterial core of every animal - the "I am" to which all messages are sent. ...
... It is all that is alive in any of us - in a mouse, in a deer, in a cocktail waitress. It is unwavering and pure, no matter what preposterous adventure may befall us. A sacred picture of Saint Anthony alone is one vertical, unwavering band of light. ...
... If a cockroach were near him, or a cocktail waitress, the picture would show two such bands of light. Our awareness is all that is alive and maybe sacred in any of us. Everything else about us is dead machinery."
In other words, Karabekian performed an heroic feat of essentialism, stripping away the unnecessary to portray the essence of life. More than mere technical skill, it is this ability that determines an artist's greatness.
Essentialism in Science
Outside of the art world, essentialism has its place among scientists, too - most popularly in an attempt to define life. Defining life is extremely complicated because not all life breathes air, not all life is aware.
The closest we've come to a definition is, "something that will go 'squish' if you step on it." - which is an exercise in essentialism itself. No hard-and-fast parameters, but basically a way of saying that you'll know it when you see it.
"You'll know it when you see it" is also our way of defining beauty. Volumes have been written on ideal ratios, symmetry and the Golden Mean, but then we're blindsided by the imperfect, asymmetrical beauty of the Japanese wabi-sabi aesthetic.
We can attempt to define beauty all we want, but it seems to be more of an indefinable quality - we acknowledge this by saying it's "in the eye of the beholder."
So what is spirituality? What differentiates spirituality from religion or faith? Is it belief in a deity, or something more basic? Is it possible to strip generic spirituality down to its essence and come up with a definition that applies every single time?
What about the meaning of life? What traits must humans have, what experiences must they be a part of to make them human, without which, they would not be human? Is it on a molecular scale, or is it something mental, or something spiritual? These are the questions that keep philosophers up at night.
As you proceed on your life journey, it can be helpful to strip things down to their essential bits. Although frequently it's an exercise in futility, it helps you gain a wider perspective and a greater understanding of triumphs and failures. And after all, isn't that at the heart of spirituality?