Gravitational wave

First, what is a gravitational wave? I find it interesting that some people are expressing difficulty in understanding what a gravitational wave is, as though everybody (who is not a physicist) has a perfectly good understanding of what any kind of wave is. We don't need to go too deeply beneath the surface, as it were, to understand this well enough to be amazed at the discovery, but not well enough to get a job being a Gravitational Waveologist. Imagine a perfectly flat pond. Imagine throwing a stone out into the middle of the pond. Now imagine ripples, tiny waves, spreading out from the…