Main Entry: bar·ri·er

Pronunciation: \ˈbar-ē-ər\

Function: noun

1 : a material object or set of objects that separates, demarcates, or serves as a barricade—see blood-brain barrier, placental barrier
2 : a factor that tends to restrict the free movement, mingling, or interbreeding of individuals or populations <behavioral and geographic barriers to hybridization>