What is the process called when cells divide by splitting in half?

The process where cells divide by splitting in half is known as fission. In the context of the given choices, while mitosis refers specifically to the process of nuclear division in eukaryotic cells, fission is a simpler form of cell division typically associated with prokaryotic organisms, such as bacteria. However, the term is often used to describe the concept of a cell's division resulting in two daughter cells.

Cytokinesis is the process that typically follows mitosis, where the cytoplasm of a parent cell divides into two daughter cells, completing the whole cell division process. Meiosis, on the other hand, is a specialized type of cellular division that reduces the chromosome number by half to produce gametes.

In this instance, if the question is generally asking about the simplest form of cell division that results in two equal halves, then fission would be the most accurate term. However, it is important to also note that in the context of eukaryotic cells, the process of mitosis is closely related and involves precise steps leading up to the division of the nucleus and consequently the entire cell.