I was asked this question in an interview.
What are functional and non functional parts of an application ?
Functional parts are those that relate to the function of the application - what it does.
Non functional are the parts that do not directly relate to the function - things like:
For example, in a calculator application, the functional parts are how the input and output work and the calculation logic/operation itself.
Non functional would be the usability, quality, performance and other aspects that do not have direct bearing on the calculator operations.