Have you ever seen anyone bowing to each other in the street or the hallways?
South Korea is a country of strict Confucian hierarchy and etiquette is very important. Therefore, the bow is the traditional Korean greeting which shows repect to other person,
But, they dont always bow to each other to say hi. they usually bow as man vs man, old man vs old man, kids vs man or kids vs old man
In some cases, only one person bow and one person doesnt like like kid vs man, kid vs old man or man vs old man. Only the yougest person bow to say hi and the oldest person just shake his/her hands or just say hi in korean. Korean poeple think it is showing respect to old people.