You know it when you see it. Its that soft, blurry, buttery background that lets the key parts of your photo come into contrasting sharp focus. Correctly pronounced, its 'boh-keh', but many just pronounce it like a group of flowers. Either is fine.
Tip: If your camera has an aperture mode (often an 'A'), select it and open your f-stop to its widest setting. Counter-intuitively, this is the smaller number, like F2 or so. When you shoot this way, you'll get the shallow depth of field associated with bokeh.