“Bokeh” is a photography term that people like to bandy about, mostly because it’s foreign (from a Japanese word), semi-obscure and makes photography seem more exclusive. It simply refers to the out-of-focus parts of a photo. Most often, though, people apply it specifically to unfocused points of light, frequently in the background of low-light photographs. Photographers argue about which cameras produce the most attractive bokeh, the merits of round light-points versus polygonal ones, and so on.
All it truly means, though, is that blurry bits of light can be really pretty.