A foreign national who during this his period of sojourn leaves Korea to return before the period of sojourn has expired, must have a Re-Entry Permit. A foreigner who leaves Korea without having obtained a Re-Entry Permit will, while overseas, have to get a new entry visa and after returning, go through the process of alien registration all over again, if you intend to stay for 90 days or more (it depends on your nationality). A foreigner who enters Korea with a multiple visa may leave Korea and return a limitless number of times during their period of sojourn without needing an additional Re-Entry Permit
Single Entry Visa :
One a single-entry is permitted for the duration of the visa
(If you leave from Korea with a visa, you cannot enter Korea again with the same
status of the visa even though it remains valid)
Multiple-entry Visa :
Multiple entries are permitted for as long as visa remains valid
