This api mash up involves google maps/places API's with your browser location.
A web Application Programming Interface or API is a interface to a request-response server, typically via JSON or XML, that can be accessed from the internet. Web applications generally mash up multiple APIs and combine them to create a sum greater than its parts.
APIs connect your website with remote services to easily enhance the end user experience by allowing a web site to access extensive databases and enhanced services that will bring your site to the next level.
A payment gateway is the equivalent of a physical point of sale terminal like what is in most retail outlets, they protect credit card details by encrypting sensitive information, such as credit card numbers, to ensure that information is passed securely between the customer and the merchant and also between merchant and the payment processor. All of this happens behind the scenes so all your end user has to do is enter in their card details.
These days they are the same as api's but i thought the site needed contenet balance, I am more doing what contenet does then content. Btw big thanks to wikipedia: