I hadn't heard the term in a while, but I believe page-flipping more specifically means that the buffer roles can be switched in hardware (e.g. by changing a "framebuffer start address" register in the CRTC or RAMDAC) instead of requiring a buffer to be copied (e.g. via a DMA or blitter operation). Both schemes are double-buffered in the sense that you're never actively rendering to the same buffer that's being scanned out, but page-flipping has significantly less overhead.