The 'describe' keyword in javascript

So I am a newbie in javascript and i had been going through some one else's code and I found this..

describe('deviceready', function() {
it('should report that it fired', function() {
spyOn(app, 'report');
app.deviceready();
expect(app.report).toHaveBeenCalledWith('deviceready');
});
});

What I don't understand is: What exactly does the describe keyword do?

info:
- Its a phonegap application
- We are using the spine.js and jQuery libraries