In article , Phil L
writes

They are 'drupes' !

A drupe is any fruit which contains a single seed, peach, olive, cherry,
plum and apricot to name a few...see he
http://www.webster-dictionary.org/definition/drupes

and plums, along with nectarines and peaches, olives and mangoes are all
part of the same family : Prunus, so you could say that they are indeed
related...see this page for more details:
http://www.fact-index.com/d/dr/drupe.html


Correction: Olives are not botanically related to plums.

Olives are in the Oleaceae family of about 20 species of plants native
to Mediterranean and similar climates, of which O.Europeaea is commonly
used for olive production.

Plums are in the wide ranging Prunus family which includes nectarines,
peaches, cherries, almonds, apricots etc., but not olives or mangoes.

Although I'm not an expert in anything :-p

Try studying a little taxonomy.
--
Alan & Joan Gould - North Lincs.