The word that refers to the shape of a bacterium is morphology.

However, you might be looking for a more specific term to describe the actual shape. Here are some common bacterial shapes:

* Coccus: Spherical or round

* Bacillus: Rod-shaped

* Spirillum: Spiral-shaped

* Vibrio: Comma-shaped

Let me know if you have a particular shape in mind, and I can help you find the right word!