Need a professional coder's opinion

Greetings all - I need some help with terminology.

I am in the process of designing specs for a new site, most of which will be developed in-house, part of which will be outsourced. The specs will be given to the outsource entity and I have one component that I don't know what to call it - not the exactly right term. It's important that it's right so I don't look like an idiot when I hand over the specs.

The part they are going to be responsible for is writing the PHP code to interpret and display the results of a request made to a database, and insert the XML results into an HTML page in a pre-defined area. My skills with PHP are limited so that's why we're having this part written by someone else.

I have been referring (in-house) to this as an "interpreter" or "interface", and others have thrown around the term "API", but I'm not sure exactly what that component should be called. I know this sounds like a very picayune question, but it really needs to be correct.

What would a professional programmer call this - any suggestions?