E-2 Visa Question?

Hey guys! I just got my passport back with my E-2 visa today. Yay!

However, as I was looking it over, I noticed that it said “single entry.” I’ve already begun making plans for traveling outside Korea while I’m there.┬áSo I’m a little confused.

Will I not be able to leave and re-enter Korea? Do I have to get another type of visa before I travel?

If anyone has any experience with this, could you please help/clarify?

I have a US passport if that makes any difference.