Cashews are the true fruit of the cashew tree. They grow at the base of a pseudofruit that looks a little like a squash, and they’re technically not a nut but a seed. Cashews are fairly readily available and have a soft, sweet flesh. They’re one of the things you’ll almost always find in commercial mixes of nuts or fruit and nut.
Are cashews paleo? That’s still open for discussion. In some ways it depends just how strict you want your paleo diet to be in terms of avoiding chemicals that may be harmful. Cashews have to be roasted or treated to remove the phenols they’re coated with, because these chemicals can inflame the digestive tract and produce skin rashes. So that’s a strike against their inclusion in a paleo diet. But Paleo authorities like Robb Wolf advocates eating cashews and they’re nutritious, as most seeds are: oilier than nuts, but still high in protein and micronutrients.
At best, cashews deserve a full place in your paleo diet, alongside your lean meats and vegetables and your other seeds and nuts. At worst, they’re a better choice than peanuts or many other unsuitable food choices. They represent at most a minor deviation from the paleo diet.