A nut harvested from trees that are grown in many of the temperate regions of the world. The nuts are oval in shape and the hard shell looks like a pair of domes that have been fused together along a ridged seam. The meat has a crisp texture and a rich flavor that is also a bit astringent or acidic, which can be removed by toasting the nuts. Walnuts are popular as a snack or as an ingredient for many desserts and savory dishes. There are several varieties of walnuts, but the most popular are the English walnut and the black walnut. They can be stored for several months if left in a cool dark place and if they are shelled, they should be stored in the refrigerator where they will keep for up to half a year. Frozen walnuts will last for a year or more.