Simplify the following text for a Grade 7 native English-speaking person.
Original: Busan ( Officially Busan Metropolitan City ) , formerly spelled Pusan is South Korea 's second largest metropolis after Seoul , with a population of around 3.6 million . It is the largest port city in South Korea and the fifth largest port in the world .
Simplified: Busan ( Pusan ) is a major port city in South Korea and is the second-largest city in the country .