A drupe is a fruit which has a soft, fleshy outer layer which covers a hard inner core, where the seeds are contains. Examples of well known drupes include peaches, plums, and nectarines.

But what about blackberries? Are blackberries considered drupes?

Yes, sort of.

Blackberries are actually drupelets, or aggregates of drupes. Drupelet is the plural form of the word drupe.

Rather than a single fruit, a blackberry is a small group of fruits that grow together, forming a drupelet.