What's a... drupe?

Or how an olive is like a peach

A drupe is a fruit in which the outer layer is a thin skin, the middle layer is thick and usually fleshy (though sometimes tough, as in the almond or fibrous, as in the coconut), and the inner layer (the pit) is hard and stony. Within the pit is usually one seed. Other representative drupes are the cherry, peach, mango, olive, and walnut. (Merriam-Webster concise encyclopedia)

In fact the botanical term is derived from the Greek word dryppa meaning olive, which I guess means a peach is like an olive.

Other terms relating to the parts of an olive you may see are as follows:

    exocarp        = skin
    mesocarp      = flesh
    endocarp      = pit
    indehiscent    = meaning the fruit does not open up to release it's seed
    lignification     = the process of the endocarp hardening as it matures