Market segmentation refers to

the philosophy that to do a truly excellent job of marketing, a company should concentrate on only one customer segment at a time.

sorting prospective buyers into groups that are willing to pay more than the cost of production for a good or service.

disaggregating prospective buyers from groups into segments of one $($individuals$)$ and then creating specific products that will satisfy this person's unique needs.

dividing & grouping prospective buyers into groups that have common needs and will respond similarly to a marketing action.

the belief that it is possible to satisfy every customer's needs if you can identify the correct segment within which they belong.