That's the biking term for when you have a day when you're just not riding well. (It's French, of course, and means basically a day without, usually without the energy or speed or whatever that bike riders want.)
That was my ride today. I chose a route with a fairly hard start, and then an easier finish. I barely (and when I say barely, I mean barely) made it up the hard start hill.
I was ready to be done five miles out, riding back against the wind.
I don't know why. I'm reasonably rested, ate decently, drank plenty, and it wasn't especially hot out (about 80F).