Simplify the following text for a Grade 10 native English-speaking person.
Original: The Atlantic Standard Time Zone ( AST ) is a geographical region that keeps time by subtracting four hours from either Coordinated Universal Time ( UTC ) or Greenwich Mean Time ( GMT ) , resulting in UTC-4 or GMT-4 .
Simplified: The Atlantic Standard Time Zone ( AST ) is a geographic region that keeps time by subtracting four hours from Greenwich Mean Time ( GMT ) , resulting in GMT-4 ( UTC-4 ) .