Japan And South Korea
South Korea And Japan, Japan And Korea, Korea And Japan
noun
With the 日 of 日本, the 日 means Japan. Then, you add Korea into the mix and you have Japan + Korea. This word means Japan and South Korea or South Korea and Japan (depending on where you're from, I guess).
にっかん
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
この風習は日韓両国でよく見られます。
This custom is frequently seen in both Japan and Korea.