Kola nuts are the seeds of the kola tree, a tree native to West Africa. In West Africa, kola nuts are chewed for their stimulating effects, and they are also used in social rituals and as a symbol of hospitality. 
The nuts are about the size of a chestnut, and they are brown and slightly flattened. When fresh, they have a bitter taste. When dried, they become milder and smell of nutmeg. 
Kola nuts are known for their bitter taste and caffeine content and have been used for various purposes, including as a stimulant, in traditional rituals, and in the original recipe for Coca-Cola. The first Coca-Cola recipe included kola nut extracts, but this is no longer the case.