Simplify the following text for a Grade 17 native English-speaking person.
Original: The Central United States is sometimes conceived as between the Eastern United States and Western United States as part of a three-region model , roughly coincident with the Midwestern United States plus the western and central portions of the Southern United States ; the term is also sometimes used more or less as a synonym for the Midwest , omitting all or most of the South .
Simplified: The Central United States is sometimes conceived as between the Eastern United States and Western United States as part of a three-region model , roughly coincident with the Midwestern United States plus the western and central portions of the Southern United States ; the term is also sometimes used more or less as a synonym for the Midwest , leaving out all or most of the South .