Most people use the terms \"folder\" and \"directory\" interchangeably. From a programmer point of view, is there a difference, and if so, what is it? Does it depend on the OS,
Your link basically describes what is different on a technical basis. Most of the times People use them interchangeably and which they choose is mostly based on what environment they come from.
Unless you are doing development cross-platform for an application that will modify files, you don't need to know the differences. As soon as you are preparing to work with several different file system types, you should know their differences.
Don't expect people to know which term to use when. I think of those terms as interchangable, since the differences are known to too few people.