According to "whatis.techtarget.com",
"front-end" application is one that application users interact with directly.
"back-end" application or program serves indirectly in support of the front-end services, usually by being closer to the required resource or having the capability to communicate with the required resource.
For example, the Telephony Application Program Interface ( TAPI ) is sometimes referred to as a front-end interface for telephone services. A program's TAPI requests are mapped by Microsoft's TAPI Dynamic Link Library programs (an intermediate set of programs) to a "back-end" program or driver that makes the more detailed series of requests to the telephone hardware in the computer.
So the next you hear these terms from some geeky nerds, you don't have to be confused. That's what I'm also telling to myself.