odata verbose or nometadata to fetch data

Hi,

What is the difference between verbose and nometadata in the odata definition for javascript client object model.

I tried the below code:

 headers: {    "accept": "application/json;odata=verbose","content-type":"application/json;odata=verbose","X-RequestDigest": $("#__REQUESTDIGEST").val()  },
	 success: function (data) {

		var items = data.d.results;

In the console , i can see the results. However, using the below code:

 headers: {    "accept": "application/json;odata=nometadata","content-type":"application/json;odata=nometadata","X-RequestDigest": $("#__REQUESTDIGEST").val()  },
	 success: function (data) {
	 	var items = data.d.results;

is showing error "Unable to get property 'results' of undefined or null reference".

How to use "nometadata" option and what is the major difference in using this?

Thanks