I saw an application built with Node.js and I don't understand how are the words describe and it available?

In the browser console it is a function and describe throws a ReferenceError.

I know that they are used for testing.

const {assert} = require('chai');
const {jsdom} = require('jsdom');

const parseTextFromHTML = (htmlAsString, selector) => {
  const selectedElement = jsdom(htmlAsString).querySelector(selector);
  if (selectedElement !== null) {
    return selectedElement.textContent;
  } else {
    throw new Error(`No element with selector ${selector} found in HTML string`);
  }
};

describe('User visits index', () => {
  describe('to post an order', () => {
    it('starts with a blank order', () => {
      browser.url('/');

      assert.equal(browser.getText('#deliver-to span'), '');
      assert.equal(browser.getText('#cake-type span'), '');
      assert.equal(browser.getText('#fillings span'), '');
      assert.equal(browser.getText('#size span'), '');
    });
  });
});