1. An intermediary computer that does set-up and filtering for another (usually more powerful but less friendly) machine (a "back end").
2. Software that provides an interface to another program "behind" it, which may not be as user-friendly. Probably from analogy with hardware front-ends that interfaced with mainframes.
To customers, the front end and the back end of the IT infrastructure are inseparable.
She showed off a newly damaged piece on the front end of the train.
On the same theory, Obama needs to want to learn about how websites work on the front end and back end.