Cashew nuts (Anacardium occidentale, aka Caju) are contained in olive pods beneath an upwards heart-shaped fruit. Only one per fruit, so no wonder they are expensive compared to peanuts.
The fruit itself has many medical and cosmetic uses. It can be eaten provided it is ripe, and the taste could be described as something between a quince and a pear, with the astringency of a quince or that of a cooking apple (British Bramley). However, they do spoil rapidly once picked.