{Quaking bog}, a bog of forming peat so saturated with water that it shakes when trodden upon. {Quaking grass}. (Bot.) (a) One of several grasses of the genus {Briza}, having slender-stalked and pendulous ovate spikelets, which quake and rattle in the wind. {Briza maxima} is the large quaking grass; {B. media} and {B. minor} are the smaller kinds. (b) Rattlesnake grass ({Glyceria Canadensis}).