Here's why:

* Coccus refers to the shape of a bacterial cell, specifically spherical or round.

* Prokaryotes are single-celled organisms that lack a nucleus and other membrane-bound organelles. Bacteria are prokaryotes.

* Eukaryotes are organisms whose cells have a nucleus and other membrane-bound organelles. Examples include plants, animals, fungi, and protists.

So, while the term "coccus" describes a shape, the classification of a coccus as prokaryotic or eukaryotic depends on the organism itself. All cocci are bacteria, and bacteria are prokaryotes.