Glaucous is a colour that is bluish-green or bluish-grey. In botany it refers to a pale bluish waxy or powdery layer on a surface such as a leaf or a fruit. In birds it refers to a pale bluish grey colour of the feathers, legs or some other part of the bird.
Glaucous appears in the name of some plants and birds. For example - Glaucous Gull, (Larus glaucescens) or Glaucous Macaw, (Anodorhynchus glaucus). In botany there is the Glaucous Sedge, (Carex flacca) and the Glaucous Michelmas Daisy, (Symphyotrichum laeve).
Often grapes, plums and other fruit have a glaucous waxy or powdery layer on the surface of their skin. That layer protects the fruit from water. It can be easily rubbed off.