What is it >> in JavaScript?

What is it >> in JavaScript?

index is a number. I do not understand what is it >> in js.
setIndex: function(index) {
var i = this.index;
this.index = index >> 0; // ?????
if (this.index < 0) {
this.index = 0;
} else if (this.index >= this.config.items.length) {
this.index = this.config.items.length - 1;
}
return (i !== this.index);
}