Difference Between ?Add Web Reference? and ?Add Service Reference?

Hi. I am using VS 2008.

I need to create a WebService / WebReference. Can anybody explain me what is the difference between WebService / WebReference. I have created a webservice and used in some of my webapplications. Its working fine, but I am not familier with the WebReference. Can anybody suggest me the difference and also to use the method I need to implement which should also be more secure and also in terms of performance.
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