When did a program turn into an app??
When they went into "the Store" and actually became CRAPP...
actually Micro-shaft has been using the term 'app' since before XP. I forget when it started, maybe around the Windows '98 time frame. They just haven't forced the REST of us to call it that until Apple's iPhone and Google's Android and their associated 'app stores' became 'a thing'.
Then it's all 'hip' and 'cool' and 'new' and 'shiny' and sounds like your dad trying to use teen lingo when you're 15.