Final answer:
The term "discordant" in twin studies refers to a pair of twins in which one twin exhibits a trait or disorder while the other does not, helping to differentiate genetic influence from environmental factors.
Step-by-step explanation:
When referring to twin studies, the term "discordant" means that one member of a twin pair has the trait or disorder and the other one does not. This is crucial in studies where researchers are trying to understand the influence of genetics versus environment on various traits and disorders. Twin studies often involve comparisons between monozygotic (identical) twins who are genetically almost identical, and any differences observed between them can provide insight into the effects of the social environment on individuals with the same genetic makeup. Discordant twins are particularly interesting to researchers because they help to separate the influence of genetics from that of the environment, as identical twins share the same DNA but can still exhibit different traits or outcomes if influenced by their environment.