Woelse and Cheonse System in South Korea

Woelse is a system where you put down a deposit (Bojeungeum / 보증금 /key money) and on top of that pay a monthly rent. Generally, the higher the deposit, the lower your rent. You get your deposit back when you leave.

If you see a realtor's ad like this:

월세

2방

200 / 40

This means a 2 room apartment for 20 million won deposit at 400,000 a month rent.

Cheonse is a system where you put down a huge deposit (typically over 100 million won, but one rooms can be had for 50-60 depending on the area) and don't pay any monthly rent. You get your deposit back when you leave.

If you see a realtor's ad like this:

천세

2방

1억

This means a 2 room apartment for 100 million won deposit.

There may be a govt registration process (mentioned above) that does offer a degree of protection for cheonsae -- up to 20 million won depending on location