How to create an XML product feed
From Spiffy Stores Knowledge Base
Setting up an XML feed for your products is a great way to get added exposure for your store by syndicating them to a variety of shopping portals.
An xml feed is a means to publish frequently updated data in a consistent data format. With product listings, that data is the product name, price, description, manufacturer, photo url’s, etc.
Since the data is in a standard format, it can sometimes be used by other sites to populate their databases of products on your behalf — automating the otherwise manual task of data entry, that would be required to place your products on those sites.