Segmentation is when something divides, or is divided, into smaller parts. You can see it in a worm: the body is a row of little units. A company may talk about market segmentation — cutting one big group of buyers into smaller groups. A computer person may talk about cutting a picture into regions, and still use this same noun. The idea is one whole marked into bits. The word is a little schoolish and workish. Everyday English more often says splitting, dividing, or cutting up. Though actually, in science class and in business English, segmentation is the normal noun; people do not hear it as fancy, just as the specialist’s word for “dividing into pieces.” It is not about keeping groups of people apart — that is segregation, a different family.