what is meaning this code in Jquery?
`$.fn.extend({
    mousewheel: function(fn) {
        return fn ? this.bind("mousewheel", fn) : this.trigger("mousewheel");
    },
    unmousewheel: function(fn) {
	return this.unbind("mousewheel", fn);
    }
});`//comment added

I don't understand this code, in particular what the bind method does.
what is meaning this code in Jquery?
===

`$.fn.extend({
    mousewheel: function(fn) {
        return fn ? this.bind("mousewheel", fn) : this.trigger("mousewheel");
    },
    unmousewheel: function(fn) {
	return this.unbind("mousewheel", fn);
    }
});`//comment added

I don't understand this code, in particular what the bind method does.