The zany world of computers. A computer application is what you need to perform actions on a computing device. With the advent of mobile computing and the need for instant gratification replies [1], "application" got shortened to "app", but if you use "app" in reference to non-mobile usage, people assume you're talking about mobile. Illogic in computer conversations is ???

[1] OK, so "app" was likely used way before mobile existed, but the current convention says it couldn't have been. ;-)