A mixture of a grape and a nut. Either a grape inside of a nut, or a nut inside of a grape. Usually either grapes are inserted into pistachio shells, or almonds or cashews are inserted into the center of a grape, but a true grut is any heterogeneous mixture of grapes and nuts.
Person A: "I'm really hungry, but all I have are some grapes and nuts. What should I do?"
Person B: "Don't worry. Insert the grape into the pistachio nut shells, and eat them. It's called a grut. They're really good."
Person A: "What else could I do with them."
Person B: "Well you can also take an almond or cashew and insert it into the center of the grape. Then you can eat it. That's another form of the grut..."