There are 2 types of segmentation:
Segmentation with a visit scope
Working on a set of visits corresponding to predefined criterion, over a given analysis period. (Example: visits from sponsored links).
Segmentation with a visitor scope (or identified visitor)
This segmentation is based on a cohort notion. A cohort is defined over a period N. It is composed of all visitors that have shared (at least once) the same visit experience during period N. (Example: visitors that came from a sponsored link last week).
All visits made by these visitors meeting this criteria (during at least one visit) will be taken into account during your analysis period.
In order to identify all visits made by the same visitor, it is possible to use the identifier of the visitor's cookie or the identified visitor's identifier. This differentiates the visitor range from the identified visitor range.