I haven't heard that term for quite some time, as most firms use "integration testing", but interface testing used to be a common term and it is different from UI (user interface) testing. The idea is that after the new application(s) are tested end-to-end, all of the interfaces that either feed or are fed the by new application(s)are tested with the new app end-to-end.
No doubt you'll get all kinds of answers here; terminology varies from company to company.
Here is another one of those terms that context is everything, or nothing depending on how you look at it.
For me, being in the Loan Origination industry, interface testing is the specific testing required to ensure that requests to outside vendors of information (Credit Scores, Debt History, etc) are handled correctly. For us that can be synchronous, asynchronous or postback communications via XSL programming/XML files.
UI testing is required to input the information as well as the verification of the data that is returned can correctly be intergrated into the system. For the most part though it is more technical in the creating of the XML file, the transmission of this file, the transmission of data returned and triggers to ensure the files are seen when they come back......
Interface Testing:Testing conducted to evaluate whether systems or components pass data and control correctly to each other.
And one example for this is the;
Integration testing where the interfaces between system components are tested thouroughly.
A unique characteristic of the testing profession is its vocabulary. The professionís vocabulary represents the knowledge of the profession and its ability to communicate with others about the professions knowledge.
But here I feel that we are running too much after simply naming different types of testing which would normally fall under basic testing types - Unit, Integration and System.
Again there are testing techniques which are the means used by testers to accomplish their test objectives.
Don't be bothered too much about what is ABC Testing and what is XYZ Testing. As long as you understand your testing objectives thouroughly, you can stick to plain ol' trusted testing terms. Spend your energy to define what exactly you are trying to test rather than just hearing from someone that we need to do "Interface Testing" and running after the jargon.