Processing is a programming language, development environment, and online community... Today, there are tens of thousands of students, artists, designers, researchers, and hobbyists who use Processing for learning, prototyping, and production.
It's a lot of things!
In Processing, a computer program is called a sketch.

// global variables go herevoid setup() {// one time stuff}void draw() {// continuous loop}
void setup() {size(500, 500); smooth();bgColor = color(255);myImage = loadImage("conor-barry.jpg");ball = new Ball(x, y, size);}
void draw() {background(100); if (mousePressed) { fill(0, 255, 0); // green } else { fill(255); // white } rectMode(CENTER); rect(width/2, height/2, 50, 50);}