In biology, particularly cell biology, the term organelle is used to describe any one of a number of types of subcellular structures, historically identified through the use of some form of microscopy.
A few large organelles probably originated from endosymbiont bacteria:
... The left-wing of the SPA, or the Debs Caucus, including McReynolds, reconstituted the spirit of the SPA and Eugene V. Debs into the Socialist Party U.S.A. (SPUSA) that ...