I was asked the other day, by a creative-type, no less, to explain the 'concept' of a day job. Specifically, why on Earth would you call your day job just that, a 'day job', if you know that you aren't going to pay the bills doing what you love for a long time, if ever. Doesn't that make it just a 'job'? "What's the point of getting a degree in something knowing full well you'll never make a living doing that?" she wondered. "Isn't that a little insane?"
"A day job is a form of occupation taken by a person in order to make ends meet while working another low-paying (or non-paying) job in their preferred career track. Archetypal examples of this are the diner waitress who is working as a waitress for her "day job", while she tries to become an actress, and the professional athlete who must work as a laborer in the off season because he is currently only able to make the roster of a semi-professional team."
one's regular job and main source of income, usually viewed in contrast to a speculative or irregular endeavor: Good luck in the lottery, but don't quit your day job.
I don't know how well either of those definitions speak to the whole 'getting-a-degree-in-something-I-know-won't-pay-the-bills' thing, and it doesn't address the whole insanity bit (which, frankly, hurt my tender little feelings), but it does call out the reality of the day job as concept, as practice, as Thing That We Must Do.
For those lucky folks who went to Rice University and popped out of undergrad with a degree in accounting that they promptly rolled into a well-paying entry-level gig, congratulations. I have no idea what that is like, and the concept of actually working full-time, 40-hours a week, five days in a row, the thing that I aspire to be doing is just a tad out of reach.
At least Dictionary.com doesn't think I'm insane. Or does it?
1. afflicted with or characteristic of mental derangement; "was declared insane"; "insane laughter" [ant: sane]
2. very foolish; "harebrained ideas"; "took insane risks behind the wheel"; "a completely mad scheme to build a bridge between two mountains"