First cousins once removed are the children of your first cousins or the parents of your first cousins. The term "once removed" indicates a difference of one generation. For example, if your first cousin has a child, that child is your first cousin once removed. Conversely, if you have a first cousin and one of your parents is a sibling to that cousin's parent, you are also considered first cousins once removed to each other. This relationship helps to clarify family connections within the broader context of family trees and genealogy, often involving terms like family, genealogy, and family tree.