"Business requirements describe business objectives. They outline the details of what a business must be able to do. Functional requirements define the functions that a solution should be able to perform. Technical requirements define how a solution will be developed.
The retail company you mentioned would have a business objective to allow customers to purchase products easily. They desire to allow customers to purchase goods through their website. Those are business requirements. There would then be a resulting set of functional requirements for a web page that allows customers to enter their credit card information. Additionally, there would be technical requirements describing the process for processing payments, updating inventory, and updating the various integrated financial systems accordingly."