They share one common characteristic: Their natural composition (without human manipulation) has less than a 50% of water. These are very energetic meals, rich in fats, proteins, as in trace elements. Depending the kind of the nut, they also can contribute with a good quantity of vitamins or omega 3 fatty acids.
It is possible to identify two large groups of nuts:
The ones covered by a solid shell.
The ones that comes from dried out nut.