Try look here
http://www.cio.com/ec/edit/b2cabc.html#difference .
B2B is business to business. For example, Citibank transacts with (e.g. calls web service of) Mastercard.
B2C is business to customer. For example, Citibank has a web site that allows customers to manage their bank account via internet. B2C usually has a 'front-end' like a website.
